diff --git a/Cargo.lock b/Cargo.lock
index 98ce744..a5f490c 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -700,7 +700,7 @@ dependencies = [
 
 [[package]]
 name = "gree-controller"
-version = "0.13.7"
+version = "0.13.8"
 dependencies = [
  "aes",
  "aes-gcm",
diff --git a/Cargo.toml b/Cargo.toml
index a435c90..d7302ae 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "gree-controller"
-version = "0.13.7"
+version = "0.13.8"
 edition = "2021"
 authors = ["GREE Controller contributors"]
 description = "Standalone local GREE HVAC controller with Web UI, SQLite and Home Assistant sensor support"
diff --git a/FILE_MANIFEST.sha256 b/FILE_MANIFEST.sha256
index 4e26824..353bf9a 100644
--- a/FILE_MANIFEST.sha256
+++ b/FILE_MANIFEST.sha256
@@ -1,13 +1,13 @@
 d67af429e4da9ce08e9d2f2a8472849ffbd70d135b1c5da535a076026794d04c  ./.env.example
 a4ec3874a2e3ab1bad28fb40bb620f7b01f64d01ad9b699306bf70ada31227db  ./.gitignore
-d4330d1b80dd2bf948a5157c97581c2ca10dc69b7d6740fd55c48a699c2e3bc6  ./Cargo.lock
-71d0ce719983e6d41bd89b592a6eaf66658479c0c30424b88d1133d80936d4aa  ./Cargo.toml
+ff8ef8ed21e7d3617f9939cd9e809bff06744ffc99202e037b2f31ade4157867  ./Cargo.lock
+fb8bbd5479705582e3aad71568ada6892bc266a56be6ec3d69647a4b8dd30b69  ./Cargo.toml
 19b2943504acb8f8de280f873a8dbec4bb6ebbe3870b158f5655d4fb8c298f5f  ./LICENSE
-a7acf66c0bbae0c6ca3faa2993b4b8ba80fec935902d0102f34693ffc96b7a19  ./README.md
-d56cfff4179a6511aa764a91c6ddebe21fcd35f36b7298e62d012e11f62bfeb9  ./build.rs
-6d42d846df9e6115acedd9ac0ba84d05689046dc3f71fb2311c074638488d8f6  ./docs/API.md
+cd7b1af125c0d65b52042a844bfe9e9575d1c5bde31ebddfc2534231a7599fbb  ./README.md
+bb549919b96b0413152dd905aec8640bb53301f07ec7d0b1be48ccbd37936fef  ./build.rs
+eff2912449a4b78e0b9eb4ff02fa6752e31abcb71fa097a46f1d7596a4500303  ./docs/API.md
 2e1e18fd8167dabfe2469c26e85cce62486c7cb6a502c63c6f6b0cd74d5885e0  ./docs/FLOW.md
-6da82ee5007330b210a1645aed7df7951f8c858e04009631e89de51f32815ecf  ./docs/openapi.json
+8f3ca55ab14f855644b3c85074400bf4a4a6b37659f4aa5dd686757a0d2bcd56  ./docs/openapi.json
 b11e581dd916676e24402112fe6896bc681abf3c94cafc85c4d3ded3f3a272a3  ./home-assistant/README.md
 f8e8559fe10fe523ac5bc9aac25c6e26e862f679d502e8f3c39f38a0a8e40911  ./home-assistant/custom_components/gree_controller/__init__.py
 3f6ef15ef58456376ac53fde7cace1ef359d6a6f7a64c5b575ad77ea6e55ccc4  ./home-assistant/custom_components/gree_controller/api.py
@@ -18,7 +18,7 @@ b7f0873109c52be9d7f09bea3dffc416103c50085e1f0680d11661a969479898  ./home-assista
 5a96fe8f5c035c34f1339370270cd078056202d09e236dec75735be11de92a7d  ./home-assistant/custom_components/gree_controller/entity_map.py
 c4fb75c246db651087900ebfc2291ff41ac87652cd6194fc0b776b0005c1cbcf  ./home-assistant/custom_components/gree_controller/icon.png
 c4fb75c246db651087900ebfc2291ff41ac87652cd6194fc0b776b0005c1cbcf  ./home-assistant/custom_components/gree_controller/logo.png
-542d58cc7f47b55c786619c831f7bcdecaa3699940f29d9a7f26f01aaa0f0547  ./home-assistant/custom_components/gree_controller/manifest.json
+9b31873cdc44b589a4230346e6cd9ee25325b431ccf06b39f07393793410bf65  ./home-assistant/custom_components/gree_controller/manifest.json
 c52a484b671ce738ecc00228a1db19a5d703f69ab27530c2896a5c2ae3b4a96f  ./home-assistant/custom_components/gree_controller/number.py
 39c4309001b75abb56234f05662bc06e077054986876f1927937edbce528ec95  ./home-assistant/custom_components/gree_controller/select.py
 cca65482e36d48035aca178121a378fe7d578d600acff267ae81a6399c0da653  ./home-assistant/custom_components/gree_controller/sensor.py
@@ -69,7 +69,7 @@ fdcd9a5055d08037278b842e7ab69265345c5811f0a06867136c511d140bb191  ./presets/wind
 804f22123cd3e8db0fac791826c8dd9f758fb866c8e3b5655fb6d25d259dccf1  ./presets/workday_comfort.json
 01952aa92b217f8eae2493b88870e2dec595100cd15c4d561ff11ae2b936c46f  ./regenerate-sha.sh
 c64b1c6deeb24f20af662bfce7fa3683703914987241107ce664fa2f6d1a9dcb  ./scripts/README.md
-b1e6a729a28eec03b38f013377d26b95669b58c035802c96ea9201cb633d87b2  ./scripts/api_dev_test.py
+615b8c7c1c085f3dba2ddc10184b2223b2106c94f7a69ccc0592bf05b2323f27  ./scripts/api_dev_test.py
 5bc736c7bc76ca80aaa406bb171d2aa91baf4c3aa8695dce0e09b888b6ab3146  ./scripts/common.sh
 6403786610ee6d2f628193c25aee0dd058d62e904aa1a31d5f62fdaae0e94b4f  ./scripts/configure-gree-network.sh
 1d6e14e26e49aa9d3527f30a23668bf8d9c48b67e6628ef686c3155c012155de  ./scripts/dev.sh
@@ -82,8 +82,8 @@ e00d211e3885e30d7fed1e43b44e6fdad40a67019060156c0641816a93e3365f  ./scripts/netw
 81345b6a0b51736bdbc98fd23199b62e4c721b4e7437e02dab7ea79b97dff29a  ./scripts/service.sh
 472db31959be29ba99247f7e9cc07a44bc090c538cd654ad8d16e094726037a3  ./scripts/smoke.sh
 b50782b3742dfbf8a319c60571c968e93fdf8547db747c759edcffae68cb98bf  ./scripts/update.sh
-6b6cab48685c56893fbe31174460254347d73a354598d0bb1f22b195df91da3e  ./src/api.rs
-5027797b9cefb9f0aa04c792e2ac9a38745c6bf1ee822f50eb70574fa6f997e2  ./src/api/assets.rs
+0da4e4fcb8e77109fd56b301472d08acbab5ad9ecfe861296153a6a5eef723b3  ./src/api.rs
+549941b91d9f9bb829f9f64345866a1a76eebcb323d15806d9d11545566dfe6b  ./src/api/assets.rs
 05c255919f7b3d81188fc5f1410be6a0037471dfc44e93bffb009f29a1e6a3fc  ./src/api/auth.rs
 9e4fc675306e111ed3db7af9822e2925d88109c31b9e309851665a975c0bd83c  ./src/api/automations.rs
 368cd843dcac970f1aa6800ba132a4bbc3429e8379ed7abf9878dcb0c633af40  ./src/api/configuration.rs
@@ -176,24 +176,25 @@ f13f1be3d5789539eba3fc1b59c14835f8c681eca7634e118fa3763a53aeee2b  ./src/queries/
 b92a6cb158b494fe145b43c7641e65f6fafff47201d7d76edbec2cfd8b94835c  ./systemd/gree-controller.service
 544a31cb2e5374227026afd6abd0d910381f3fca1638154ebd74e3c3d96a35d1  ./web/404.html
 e98bdd7204349cce1ec6f57283509697af0bbc72280622a6c3efa6fed242db4f  ./web/favicon.svg
-9e98df7a759bd76bc7682b23c3c4b7e29f7bde972f03ae316ba7f8159301e2c6  ./web/index.html
+2808c2152a3dc56d80c158980f2a00d73e078b16731bdff240a62431ca95dea9  ./web/index.html
 9ba3f6fa05b72aa989139b2a909982571b2a02055052e4c40104f1e81a9aa7eb  ./web/js/README.md
 f272912f6e5d8b34786827d78ba592513e3ca1e85e07e4c073089c5bbb75f282  ./web/js/bootstrap.js
 badde8a5214a0322b2c45803c02a1cb723d53b25e57c687369cd804f509d9744  ./web/js/charts.js
-dd596b3362643b96be8537b9415e8c1be90d7cf458124b61121016a6742951c7  ./web/js/core.js
+ff427103d12cb99977cf1b32e6978506b6ee5179a10568b13673292c13ae3b65  ./web/js/core.js
 d880ffdac6aa07cd10d79fbacf12f87eb4c69b48a80564bbfdd0248abe8884d5  ./web/js/dashboard.js
 6c0d310e39a1e1f618a31fbdf5560a850023bf2219d897c69d636d0179dff004  ./web/js/entities.js
 0a23ac65a4a0bd113a9f78fe1d25621d6a178e10aaca53e5df8df87587998cb4  ./web/js/events.js
 2e822a00b5a6941b6a251eaf2c54ca95a53399b5d1056f3d8240e11f82d6065f  ./web/js/flows.js
 cf1ebf3b9d666f309a1add070b4da86be86d990b02c8d6474f6d121c6d332746  ./web/js/forms.js
 dbf36223863ba882c03eccea4516ba8db7acf0c2e72c6c64490cb994f1e20f96  ./web/js/history.js
-7eaa04992ea828dc89f5eaebf674cbbfd160f53eb8d0d6ef0d4e47bd8c28c435  ./web/js/main.js
+e934dbe7810da4565a4474338955b044448f3a268160e55bf98afefa4b2d97de  ./web/js/main.js
 733fcc595ed9c03c9639acc6caba46f0588f29e0b95bf72891e34443e7aa9db8  ./web/js/navigation.js
 e0a6b5d2900f5524dba395b97288f8d75976e31b27e26810d42febbfd723085c  ./web/js/realtime.js
 c8c82e88c3715b1bfabf155e36266a4c94f5e2fc03eb39dcdd9d08a1985a997c  ./web/js/router.js
 25f5c9a0aa8622f419b05f64712c9eca4896f0e79818616904b83051fd77b07b  ./web/js/settings-ui.js
 4aadfdf107593d32ab73514688f225bf559fd5ce6bbf9d9459a8098daf1fbe3d  ./web/js/settings.js
+3815fea7ae1694568c2f249bc8460e0563ced6bde89214f74f21b41fe8cad9a6  ./web/lang-init.js
 6b653e4fe2d4db4ffae6ff8f39b8ce57a10a990dc0000ee4aae51d949afadd52  ./web/manifest.webmanifest
-0b9774bb388158e23f8c90297d70659a015e0db58d25eadcae316a49e3c9fcb7  ./web/styles.css
-ae1b03f30b494f474a781a5d32072f1e73eba2b7c768109fc1cc8028cb6662a4  ./web/sw.js
+8ea4f5cf1ebdf3894e17457020bde6d5fae324eadcc0ff35a6ac4efe5d5b2b6a  ./web/styles.css
+fefdf12cbbb0a5d8a2cb89275cae28455aa42aaf179542305cc8f5e0f4825898  ./web/sw.js
 d505d793ce7cc9485b45b78bba1c0d51887adc7451ab59a42702946e5b991382  ./web/theme-init.js
diff --git a/README.md b/README.md
index 2ebc013..661fd63 100644
--- a/README.md
+++ b/README.md
@@ -2,9 +2,9 @@
 
 Self-hosted controller for GREE-compatible air conditioners with a local Web UI, thermostat zones, schedules, Home Assistant integration, history, notifications and a documented HTTP/WebSocket API.
 
-**Current release: 0.13.7**
+**Current release: 0.13.8**
 
-Release 0.13.7 consolidates the Web UI startup snapshot: `/api/bootstrap` now includes the same redacted settings views exposed by the split settings endpoints, eliminating redundant startup/resync requests while keeping the functional settings API unchanged. Bootstrap/system response construction and WebSocket state application are also deduplicated.
+Release 0.13.8 removes the visible English-to-selected-language flash during Web UI startup. A dedicated `lang-init.js` applies the preferred language before first paint, the application is revealed only after localization initialization, and content-versioned language packs can use the browser cache safely.
 
 Release 0.13.6 adds a dedicated notification toggle for GREE vs Home Assistant room-temperature discrepancies. Disabling this alert suppresses `zone.sensor_discrepancy` notifications only; sensor fallback and thermostat safety behavior are unchanged.
 
diff --git a/build.rs b/build.rs
index e8a4490..2f6d560 100644
--- a/build.rs
+++ b/build.rs
@@ -78,6 +78,7 @@ fn main() {
     println!("cargo:rerun-if-changed={}", preset_dir.display());
 
     let theme_init_path = web_dir.join("theme-init.js");
+    let lang_init_path = web_dir.join("lang-init.js");
     let styles_path = web_dir.join("styles.css");
     let index_path = web_dir.join("index.html");
     let not_found_path = web_dir.join("404.html");
@@ -86,6 +87,7 @@ fn main() {
     let favicon_path = web_dir.join("favicon.svg");
     for path in [
         &theme_init_path,
+        &lang_init_path,
         &styles_path,
         &index_path,
         &not_found_path,
@@ -100,17 +102,22 @@ fn main() {
     let app_js_hash = content_hash(app_js.as_bytes());
     let theme_init_bytes = fs::read(&theme_init_path)
         .unwrap_or_else(|error| panic!("cannot read {}: {error}", theme_init_path.display()));
+    let lang_init_bytes = fs::read(&lang_init_path)
+        .unwrap_or_else(|error| panic!("cannot read {}: {error}", lang_init_path.display()));
     let styles_bytes = fs::read(&styles_path)
         .unwrap_or_else(|error| panic!("cannot read {}: {error}", styles_path.display()));
     let theme_init_hash = content_hash(&theme_init_bytes);
+    let lang_init_hash = content_hash(&lang_init_bytes);
     let styles_hash = content_hash(&styles_bytes);
     let app_js_asset_path = format!("/app-{}.js", &app_js_hash[..12]);
     let theme_init_asset_path = format!("/theme-init-{}.js", &theme_init_hash[..12]);
+    let lang_init_asset_path = format!("/lang-init-{}.js", &lang_init_hash[..12]);
     let styles_asset_path = format!("/styles-{}.css", &styles_hash[..12]);
 
     let mut build_hash = fnv1a_update(0xcbf29ce484222325u64, app_js.as_bytes());
     for path in [
         &theme_init_path,
+        &lang_init_path,
         &styles_path,
         &index_path,
         &not_found_path,
@@ -189,12 +196,13 @@ fn main() {
             has_english = true;
         }
 
+        let language_hash = content_hash(source.as_bytes());
         manifest_languages.push(json!({
             "code": code,
             "name": name,
             "native_name": native_name,
             "locale": locale,
-            "path": format!("lang/{code}.json")
+            "path": format!("lang/{code}.json?v={}", &language_hash[..12])
         }));
         assets.push((code.to_owned(), path));
     }
@@ -298,6 +306,10 @@ fn main() {
         "pub const THEME_INIT_ASSET_PATH: &str = {:?};\n",
         theme_init_asset_path
     ));
+    generated.push_str(&format!(
+        "pub const LANG_INIT_ASSET_PATH: &str = {:?};\n",
+        lang_init_asset_path
+    ));
     generated.push_str(&format!(
         "pub const STYLES_CSS_ASSET_PATH: &str = {:?};\n",
         styles_asset_path
diff --git a/docs/API.md b/docs/API.md
index 2472718..4f2705b 100644
--- a/docs/API.md
+++ b/docs/API.md
@@ -1,6 +1,6 @@
 # GREE Controller API reference
 
-HTTP and WebSocket API for GREE Controller **0.13.7**.
+HTTP and WebSocket API for GREE Controller **0.13.8**.
 
 [← Main documentation](../README.md)
 
@@ -48,6 +48,7 @@ GET /
 GET /index.html
 GET /app.js
 GET /theme-init.js
+GET /lang-init.js
 GET /styles.css
 GET /manifest.webmanifest
 GET /sw.js
@@ -231,7 +232,7 @@ Response:
 {
   "status": "ok",
   "name": "gree-controller",
-  "version": "0.13.7",
+  "version": "0.13.8",
   "uptime_seconds": 1234,
   "control_ready": true,
   "time": "2026-08-30T06:54:00Z"
@@ -294,7 +295,7 @@ Returns the initial Web UI snapshot:
   "control_plan": {"generated_at": "2026-09-04T08:00:00Z", "zones": [], "rules": []},
   "control_plan_revision": 42,
   "system": {
-    "version": "0.13.7",
+    "version": "0.13.8",
     "uptime_seconds": 1234,
     "auth_required": false,
     "control_ready": true,
diff --git a/docs/openapi.json b/docs/openapi.json
index 7698984..1ef06d6 100644
--- a/docs/openapi.json
+++ b/docs/openapi.json
@@ -2,9 +2,9 @@
   "openapi": "3.1.0",
   "info": {
     "title": "GREE Controller API",
-    "version": "0.13.7",
+    "version": "0.13.8",
     "summary": "Local HTTP/WebSocket API for GREE HVAC control",
-    "description": "Self-hosted API used by the GREE Controller Web UI and Home Assistant integration.\n\n### Authentication\nNormal administrator endpoints accept `Authorization: Bearer <APP_TOKEN>` or `x-api-token: <APP_TOKEN>` when `GREE_CONTROLLER_APP_TOKEN` is configured. If the app token is empty, those endpoints intentionally run in trusted-LAN mode without authentication.\n\nThe restricted `/api/integrations/home-assistant/*` control surface always requires either a generated access token or the administrator app token. Generated tokens do **not** grant normal administrator API access.\n\nIn Swagger UI use **Authorize** and enter the token in either the bearer field or `x-api-token` field.\n\n### Control ownership\nThermostat zones, groups, house rules, direct device control, schedules and visual Flows share an ownership/arbitration model. Prefer zone/group/house endpoints for thermostat intent; direct device commands are technical/manual control and can deliberately take ownership.\n\n### 0.12.0 breaking API\nRuntime settings are split into functional `/api/settings/*` resources. The former `/api/settings`, `/api/debug`, `/api/events/retention`, `/api/settings/export` and `/api/settings/import` endpoints were removed without compatibility aliases.\n\n### 0.13.0\n`control-plan` keeps its existing HTTP response shape but is materialized in memory and pushed to WebSocket clients as `control_plan.updated`; HTTP remains the fallback/resync path. A restricted Home Assistant snapshot endpoint combines devices, groups and the control plan.\n\n### 0.13.1\nRuntime WebSocket churn is reduced without changing contracts: no-op zone regulator heartbeats are deduplicated and device heartbeat polls only invalidate the materialized control plan when plan-relevant device state changes.\n\n### 0.13.2\nCompletes live WebSocket synchronization for entity creation, schedules, automations, configuration imports and runtime device/automation state while preserving the existing HTTP API contracts and control-plan fallback behavior.\n\n### 0.13.3\nLogical thermostat targets are normalized to 0.1 C consistently, including Temporary Quick Thermostat and thermostat-managed automation/Flow actions. The bundled Web UI accepts comma or dot decimal input for the temporary thermostat target; physical GREE setpoint rounding is unchanged.\n\n### 0.13.4\nDisabled-zone thermostat controls remain visually active in the bundled Web UI because explicit temporary/manual thermostat and direct manual control remain available while zone automation is disabled. HTTP and WebSocket contracts are unchanged.\n\n### 0.13.5\nThe zone settings dialog now explains directly beside the enabled/disabled option that disabling a zone stops automation but does not block manual thermostat, temporary thermostat or direct manual control. HTTP and WebSocket contracts remain unchanged.\n\n### 0.13.6\nNotification settings add a dedicated sensor_discrepancy alert type for GREE vs Home Assistant room-temperature divergence. Disabling it suppresses only that notification; the GREE safety fallback remains active.\n\n### 0.13.7\nThe bootstrap snapshot now embeds all eight redacted runtime settings views. The bundled Web UI consumes those settings directly for HTTP startup and WebSocket resynchronization, removing the previous settings-request fan-out while preserving the split settings endpoints for direct reads and writes.",
+    "description": "Self-hosted API used by the GREE Controller Web UI and Home Assistant integration.\n\n### Authentication\nNormal administrator endpoints accept `Authorization: Bearer <APP_TOKEN>` or `x-api-token: <APP_TOKEN>` when `GREE_CONTROLLER_APP_TOKEN` is configured. If the app token is empty, those endpoints intentionally run in trusted-LAN mode without authentication.\n\nThe restricted `/api/integrations/home-assistant/*` control surface always requires either a generated access token or the administrator app token. Generated tokens do **not** grant normal administrator API access.\n\nIn Swagger UI use **Authorize** and enter the token in either the bearer field or `x-api-token` field.\n\n### Control ownership\nThermostat zones, groups, house rules, direct device control, schedules and visual Flows share an ownership/arbitration model. Prefer zone/group/house endpoints for thermostat intent; direct device commands are technical/manual control and can deliberately take ownership.\n\n### 0.12.0 breaking API\nRuntime settings are split into functional `/api/settings/*` resources. The former `/api/settings`, `/api/debug`, `/api/events/retention`, `/api/settings/export` and `/api/settings/import` endpoints were removed without compatibility aliases.\n\n### 0.13.0\n`control-plan` keeps its existing HTTP response shape but is materialized in memory and pushed to WebSocket clients as `control_plan.updated`; HTTP remains the fallback/resync path. A restricted Home Assistant snapshot endpoint combines devices, groups and the control plan.\n\n### 0.13.1\nRuntime WebSocket churn is reduced without changing contracts: no-op zone regulator heartbeats are deduplicated and device heartbeat polls only invalidate the materialized control plan when plan-relevant device state changes.\n\n### 0.13.2\nCompletes live WebSocket synchronization for entity creation, schedules, automations, configuration imports and runtime device/automation state while preserving the existing HTTP API contracts and control-plan fallback behavior.\n\n### 0.13.3\nLogical thermostat targets are normalized to 0.1 C consistently, including Temporary Quick Thermostat and thermostat-managed automation/Flow actions. The bundled Web UI accepts comma or dot decimal input for the temporary thermostat target; physical GREE setpoint rounding is unchanged.\n\n### 0.13.4\nDisabled-zone thermostat controls remain visually active in the bundled Web UI because explicit temporary/manual thermostat and direct manual control remain available while zone automation is disabled. HTTP and WebSocket contracts are unchanged.\n\n### 0.13.5\nThe zone settings dialog now explains directly beside the enabled/disabled option that disabling a zone stops automation but does not block manual thermostat, temporary thermostat or direct manual control. HTTP and WebSocket contracts remain unchanged.\n\n### 0.13.6\nNotification settings add a dedicated sensor_discrepancy alert type for GREE vs Home Assistant room-temperature divergence. Disabling it suppresses only that notification; the GREE safety fallback remains active.\n\n### 0.13.7\nThe bootstrap snapshot now embeds all eight redacted runtime settings views. The bundled Web UI consumes those settings directly for HTTP startup and WebSocket resynchronization, removing the previous settings-request fan-out while preserving the split settings endpoints for direct reads and writes.\n\n### 0.13.8\nThe bundled Web UI suppresses the initial English-to-selected-language flash with a dedicated pre-paint language initializer and reveals the application only after localization is initialized. Language-pack URLs are content-versioned so immutable browser caching stays safe across updates.",
     "license": {
       "name": "MIT"
     }
@@ -4891,7 +4891,7 @@
           },
           "version": {
             "type": "string",
-            "example": "0.13.7"
+            "example": "0.13.8"
           },
           "uptime_seconds": {
             "type": "integer",
diff --git a/home-assistant/custom_components/gree_controller/manifest.json b/home-assistant/custom_components/gree_controller/manifest.json
index d807461..e79707f 100644
--- a/home-assistant/custom_components/gree_controller/manifest.json
+++ b/home-assistant/custom_components/gree_controller/manifest.json
@@ -1,7 +1,7 @@
 {
   "domain": "gree_controller",
   "name": "GREE Controller",
-  "version": "0.13.7",
+  "version": "0.13.8",
   "config_flow": true,
   "integration_type": "hub",
   "iot_class": "local_polling",
diff --git a/scripts/api_dev_test.py b/scripts/api_dev_test.py
index 4cfce31..c36eb80 100644
--- a/scripts/api_dev_test.py
+++ b/scripts/api_dev_test.py
@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-"""Developer smoke/integration tests for GREE Controller API 0.13.7.
+"""Developer smoke/integration tests for GREE Controller API 0.13.8.
 
 Default mode is read-only and safe to run against a real controller.
 Use --settings-write to additionally round-trip all split settings resources and
@@ -26,7 +26,7 @@ from typing import Any, Callable, Iterable, Optional
 
 DEFAULT_BASE_URL = os.environ.get("GREE_API_URL", "http://127.0.0.1:8787")
 DEFAULT_TOKEN = os.environ.get("GREE_API_TOKEN", "")
-DEFAULT_EXPECTED_VERSION = "0.13.7"
+DEFAULT_EXPECTED_VERSION = "0.13.8"
 
 SETTINGS_PATHS: dict[str, set[str]] = {
     "/api/settings/application": {"simulator_enabled"},
@@ -553,7 +553,7 @@ def run_suite(args: argparse.Namespace) -> int:
     print(f"Settings write tests: {'ENABLED' if args.settings_write else 'disabled'}\n")
 
     runner.run("public health", lambda: test_health(client, args.expected_version))
-    runner.run("OpenAPI 0.13.7 contract", lambda: test_openapi(client, args.expected_version))
+    runner.run("OpenAPI 0.13.8 contract", lambda: test_openapi(client, args.expected_version))
     runner.run("bootstrap snapshot contract", lambda: test_bootstrap_contract(client))
     runner.run("protected API requires auth", lambda: test_protected_auth(client))
 
@@ -622,7 +622,7 @@ def run_suite(args: argparse.Namespace) -> int:
 
 def parse_args(argv: Optional[Iterable[str]] = None) -> argparse.Namespace:
     parser = argparse.ArgumentParser(
-        description="Developer smoke/integration tests for GREE Controller API 0.13.7.",
+        description="Developer smoke/integration tests for GREE Controller API 0.13.8.",
         formatter_class=argparse.RawDescriptionHelpFormatter,
         epilog="""Examples:
   python3 scripts/api_dev_test.py
diff --git a/src/api.rs b/src/api.rs
index 4b42c83..47f308c 100644
--- a/src/api.rs
+++ b/src/api.rs
@@ -50,6 +50,7 @@ const INDEX_HTML: &str = include_str!("../web/index.html");
 const NOT_FOUND_HTML: &str = include_str!("../web/404.html");
 const APP_JS: &str = include_str!(concat!(env!("OUT_DIR"), "/app.bundle.js"));
 const THEME_INIT_JS: &str = include_str!("../web/theme-init.js");
+const LANG_INIT_JS: &str = include_str!("../web/lang-init.js");
 const STYLES_CSS: &str = include_str!("../web/styles.css");
 const MANIFEST: &str = include_str!("../web/manifest.webmanifest");
 const SERVICE_WORKER: &str = include_str!("../web/sw.js");
@@ -257,6 +258,7 @@ pub fn router(state: AppState) -> Router {
         .route("/index.html", get(index))
         .route(APP_JS_ASSET_PATH, get(app_js))
         .route(THEME_INIT_ASSET_PATH, get(theme_init_js))
+        .route(LANG_INIT_ASSET_PATH, get(lang_init_js))
         .route(STYLES_CSS_ASSET_PATH, get(styles_css))
         .route("/manifest.webmanifest", get(manifest))
         .route("/sw.js", get(service_worker))
diff --git a/src/api/assets.rs b/src/api/assets.rs
index c699ac4..3e9d00a 100644
--- a/src/api/assets.rs
+++ b/src/api/assets.rs
@@ -38,6 +38,10 @@ async fn index(State(state): State<AppState>, headers: HeaderMap) -> Response {
             "__GREE_THEME_INIT_ASSET__",
             &format!("{base}{THEME_INIT_ASSET_PATH}"),
         )
+        .replace(
+            "__GREE_LANG_INIT_ASSET__",
+            &format!("{base}{LANG_INIT_ASSET_PATH}"),
+        )
         .replace(
             "__GREE_STYLES_ASSET__",
             &format!("{base}{STYLES_CSS_ASSET_PATH}"),
@@ -95,6 +99,13 @@ async fn theme_init_js() -> Response {
         "public, max-age=31536000, immutable",
     )
 }
+async fn lang_init_js() -> Response {
+    static_response(
+        LANG_INIT_JS,
+        "application/javascript; charset=utf-8",
+        "public, max-age=31536000, immutable",
+    )
+}
 async fn styles_css() -> Response {
     static_response(
         STYLES_CSS,
@@ -114,6 +125,7 @@ async fn service_worker() -> Response {
         .replace("__GREE_ASSET_CACHE__", ASSET_BUILD_ID)
         .replace("__GREE_APP_ASSET__", APP_JS_ASSET_PATH)
         .replace("__GREE_THEME_INIT_ASSET__", THEME_INIT_ASSET_PATH)
+        .replace("__GREE_LANG_INIT_ASSET__", LANG_INIT_ASSET_PATH)
         .replace("__GREE_STYLES_ASSET__", STYLES_CSS_ASSET_PATH);
     owned_response(body, "application/javascript; charset=utf-8", "no-cache")
 }
@@ -133,7 +145,7 @@ async fn language_file(Path(file): Path<String>) -> Response {
         .iter()
         .find(|(language, _)| *language == code)
     {
-        return static_response(*body, "application/json; charset=utf-8", "no-cache");
+        return static_response(*body, "application/json; charset=utf-8", "public, max-age=31536000, immutable");
     }
     let mut response = Response::new(Body::from("Language not found"));
     *response.status_mut() = StatusCode::NOT_FOUND;
diff --git a/web/index.html b/web/index.html
index 7762466..c990d2d 100644
--- a/web/index.html
+++ b/web/index.html
@@ -10,6 +10,7 @@
   <link rel="icon" href="__GREE_BASE_PATH__/favicon.svg" type="image/svg+xml">
   <link rel="stylesheet" href="__GREE_STYLES_ASSET__">
   <script src="__GREE_THEME_INIT_ASSET__"></script>
+  <script src="__GREE_LANG_INIT_ASSET__"></script>
   <title>GREE Controller</title>
 </head>
 
diff --git a/web/js/core.js b/web/js/core.js
index 3de703d..a374eaf 100644
--- a/web/js/core.js
+++ b/web/js/core.js
@@ -265,19 +265,14 @@ function renderLanguageOptions() {
 
 async function loadLanguages() {
   try {
-    const languageNonce = Date.now().toString(36);
-    const languageUrl = path => {
-      const separator = String(path).includes('?') ? '&' : '?';
-      return `${withBase(path)}${separator}v=${languageNonce}`;
-    };
-    const response = await fetch(languageUrl('/lang/index.json'), { cache: 'no-store' });
+    const response = await fetch(withBase('/lang/index.json'));
     if (!response.ok) throw new Error(`Language index HTTP ${response.status}`);
     const manifest = await response.json();
     const languages = Array.isArray(manifest.languages) ? manifest.languages : [];
     if (!languages.some(item => item.code === DEFAULT_LANGUAGE)) throw new Error('Default English language pack is missing');
 
     const loaded = await Promise.all(languages.map(async item => {
-      const packResponse = await fetch(languageUrl(item.path || `/lang/${encodeURIComponent(item.code)}.json`), { cache: 'no-store' });
+      const packResponse = await fetch(withBase(item.path || `/lang/${encodeURIComponent(item.code)}.json`));
       if (!packResponse.ok) throw new Error(`Language ${item.code} HTTP ${packResponse.status}`);
       const pack = await packResponse.json();
       return { item, pack };
diff --git a/web/js/main.js b/web/js/main.js
index 88c953a..06fdafd 100644
--- a/web/js/main.js
+++ b/web/js/main.js
@@ -4,10 +4,14 @@ window.matchMedia('(prefers-color-scheme: light)').addEventListener('change', ()
 if ('serviceWorker' in navigator) window.addEventListener('load', () => navigator.serviceWorker.register(withBase('/sw.js')).catch(() => { }));
 
 async function startApplication() {
-  observeTopbarHeight();
-  applyTheme();
-  await loadLanguages();
-  applyTranslations();
+  try {
+    observeTopbarHeight();
+    applyTheme();
+    await loadLanguages();
+    applyTranslations();
+  } finally {
+    document.documentElement.classList.remove('i18n-loading');
+  }
   setupFormUx();
   updateZoneSensorFields();
   updateSchedulePresetField();
diff --git a/web/lang-init.js b/web/lang-init.js
new file mode 100644
index 0000000..416a933
--- /dev/null
+++ b/web/lang-init.js
@@ -0,0 +1,7 @@
+'use strict';
+(() => {
+  const row = document.cookie.split('; ').find(item => item.startsWith('gree_controller_language='));
+  const language = row ? decodeURIComponent(row.split('=').slice(1).join('=')) : 'en';
+  document.documentElement.lang = language || 'en';
+  document.documentElement.classList.add('i18n-loading');
+})();
diff --git a/web/styles.css b/web/styles.css
index 64607e8..b9cd152 100644
--- a/web/styles.css
+++ b/web/styles.css
@@ -95,6 +95,10 @@ body {
   color: var(--text);
 }
 
+html.i18n-loading body {
+  visibility: hidden;
+}
+
 button,
 input,
 select {
diff --git a/web/sw.js b/web/sw.js
index 34f3214..9513b9e 100644
--- a/web/sw.js
+++ b/web/sw.js
@@ -1,7 +1,7 @@
 const CACHE = 'gree-controller-__GREE_ASSET_CACHE__';
 const SCOPE = new URL(self.registration.scope).pathname.replace(/\/$/, '');
 const path = value => `${SCOPE}${value.startsWith('/') ? value : `/${value}`}` || '/';
-const ASSETS = [path('__GREE_STYLES_ASSET__'), path('__GREE_APP_ASSET__'), path('__GREE_THEME_INIT_ASSET__'), path('/favicon.svg'), path('/manifest.webmanifest')];
+const ASSETS = [path('__GREE_STYLES_ASSET__'), path('__GREE_APP_ASSET__'), path('__GREE_THEME_INIT_ASSET__'), path('__GREE_LANG_INIT_ASSET__'), path('/favicon.svg'), path('/manifest.webmanifest')];
 self.addEventListener('install', event => event.waitUntil(caches.open(CACHE).then(cache => cache.addAll(ASSETS)).then(() => self.skipWaiting())));
 self.addEventListener('activate', event => event.waitUntil(caches.keys().then(keys => Promise.all(keys.filter(key => key !== CACHE).map(key => caches.delete(key)))).then(() => self.clients.claim())));
 self.addEventListener('fetch', event => {