add first run lang detection

client/ui/frontend/CLAUDE.md

@@ -113,7 +113,7 @@ The `ViewModeProvider` (`src/lib/viewMode.tsx`, mounted in `AppLayout`) owns a `
 
 Bootstrap lives in `src/lib/i18n.ts` and is awaited before render in `app.tsx`. It reads the current language from `Preferences.Get()`, statically imports every bundle JSON (`en/common.json`, `de/common.json`, `hu/common.json` today) from the shared tree at `client/ui/i18n/locales/` (sibling of the Go i18n package — same JSON drives both tray and React), initialises i18next with `fallbackLng: "en"` and `interpolation: { prefix: "{", suffix: "}" }`, and subscribes to the `netbird:preferences:changed` Wails event so a flip from any window (tray, settings, another renderer) calls `i18next.changeLanguage` here.
 
-**No first-run detection.** When no preferences file exists, `Preferences.Get()` returns `{language: "en"}` from the Go-side in-memory default. The frontend treats `en` as the fallback (i18next `fallbackLng: "en"`) and users pick a different language via the picker in `SettingsGeneral`. The Go store persists on the first explicit `SetLanguage`.
+**First-run browser-language detection.** When no preferences file exists, `Preferences.Get()` returns `language: ""` (the Go-side "unset" signal — `preferences.Store` no longer pre-fills a default). `initI18n` walks `navigator.language` + `navigator.languages`, lowercases each tag, and picks the first base code (`de` from `de-DE`) that has a shipped bundle — then calls `Preferences.SetLanguage(detected)` fire-and-forget so the next launch reads it back without re-detecting. If nothing matches (or the store is unreachable) the session falls through to `en`. From the second launch onward, the Go-side persisted value wins and detection is skipped. The tray (`localizer.go`) treats empty as English via its own fallback to `i18n.DefaultLanguage` so the first menu render before SetLanguage round-trips is still readable.
 
 The frontend deliberately uses **no `localStorage` / `sessionStorage` / cookies anywhere** — persistence is the Go side's job (settings via `SettingsContext.save → SetConfig`, language via `Preferences.SetLanguage`). The previous wide-panel and settings-tab persistence experiments were removed; every window opens at its baseline state.
 

client/ui/frontend/src/lib/i18n.ts

@@ -3,6 +3,7 @@ import { initReactI18next } from "react-i18next";
 import { Events } from "@wailsio/runtime";
 
 import { Preferences, I18n } from "@bindings/services";
+import { LanguageCode } from "@bindings/i18n/models.js";
 
 // Vite glob-imports every shipped bundle at build time. The locales tree
 // lives outside `frontend/` (at `client/ui/i18n/locales`) so the Go tray
@@ -27,21 +28,51 @@ for (const path in bundleModules) {
     }
 }
 
+// detectBrowserLanguage walks navigator.language + navigator.languages
+// and returns the first base code ("de" from "de-DE") that has a shipped
+// bundle. Returns null when none match, so the caller can fall back to
+// English. We only ever match against the lowercased base — region tags
+// don't have separate bundles today.
+function detectBrowserLanguage(available: string[]): string | null {
+    const tags = [navigator.language, ...(navigator.languages ?? [])].filter(
+        (tag): tag is string => typeof tag === "string" && tag.length > 0,
+    );
+    for (const tag of tags) {
+        const base = tag.toLowerCase().split("-")[0];
+        if (available.includes(base)) return base;
+    }
+    return null;
+}
+
 // initI18n is awaited from app.tsx before the first render. The Go-side
-// preferences.Store returns the in-memory default "en" when no on-disk
-// preferences file exists; if Get() rejects (daemon unreachable) we also
-// fall through with "en" so the UI still renders.
+// preferences.Store returns an empty language code when no preference has
+// ever been persisted — that's the signal for first-run browser-locale
+// detection. We pick a shipped bundle that matches navigator.language /
+// navigator.languages (falling back to "en" when nothing matches) and
+// fire-and-forget the persist via Preferences.SetLanguage so subsequent
+// launches read the value back without re-detecting.
 export async function initI18n(): Promise<void> {
+    const available = Object.keys(resources);
     let language = "en";
+    let firstRun = false;
     try {
         const prefs = await Preferences.Get();
         if (prefs?.language) {
             language = prefs.language;
+        } else {
+            firstRun = true;
+            language = detectBrowserLanguage(available) ?? "en";
         }
     } catch {
         // Daemon / preferences store unreachable — fall through with "en".
     }
 
+    if (firstRun) {
+        // Fire-and-forget: the chosen language already drives this session;
+        // persisting just locks it in so the next launch skips detection.
+        void Preferences.SetLanguage(language as LanguageCode).catch(() => {});
+    }
+
     await i18next.use(initReactI18next).init({
         lng: language,
         fallbackLng: "en",

client/ui/preferences/store.go

@@ -111,11 +111,16 @@ func NewStore(validator LanguageValidator, emitter Emitter) (*Store, error) {
 		return nil, fmt.Errorf("resolve preferences path: %w", err)
 	}
 
+	// Language starts empty — the absence of a value is the signal the
+	// frontend uses on first launch to detect the browser locale and call
+	// SetLanguage. Consumers that need an effective language (tray
+	// Localizer, i18n.Bundle.Translate) already fall back to
+	// i18n.DefaultLanguage when the code is empty.
 	s := &Store{
 		path:      path,
 		validator: validator,
 		emitter:   emitter,
-		current:   UIPreferences{Language: i18n.DefaultLanguage, ViewMode: DefaultViewMode},
+		current:   UIPreferences{ViewMode: DefaultViewMode},
 	}
 
 	if err := s.load(); err != nil {
@@ -222,9 +227,6 @@ func (s *Store) load() error {
 		return err
 	}
 
-	if loaded.Language == "" {
-		loaded.Language = i18n.DefaultLanguage
-	}
 	if !loaded.ViewMode.IsValid() {
 		loaded.ViewMode = DefaultViewMode
 	}

client/ui/preferences/store_test.go

@@ -79,7 +79,8 @@ func TestStore_DefaultsWhenFileMissing(t *testing.T) {
 	require.NoError(t, err)
 
 	got := s.Get()
-	assert.Equal(t, i18n.DefaultLanguage, got.Language, "default language should be served when no file is on disk")
+	assert.Equal(t, i18n.LanguageCode(""), got.Language, "language must be empty when no file is on disk so the frontend can detect the browser locale")
+	assert.Equal(t, DefaultViewMode, got.ViewMode, "view-mode default should still apply")
 }
 
 func TestStore_SetLanguagePersistsAndBroadcasts(t *testing.T) {
@@ -153,13 +154,17 @@ func TestStore_SetLanguageIdempotent(t *testing.T) {
 	s, err := NewStore(fakeValidator{ok: map[i18n.LanguageCode]bool{"en": true}}, emitter)
 	require.NoError(t, err)
 
+	// First call goes from "" (unset) to "en" — real change, one broadcast.
 	require.NoError(t, s.SetLanguage("en"))
+	require.Len(t, emitter.calledWith(EventPreferencesChanged), 1,
+		"first SetLanguage from unset should broadcast")
 
-	// SetLanguage to the current value is a no-op — no disk write, no
-	// broadcast. Without this guard the tray would re-render the menu on
-	// every cosmetic re-save of the preferences file.
-	assert.Empty(t, emitter.calledWith(EventPreferencesChanged),
-		"setting the current language should not broadcast")
+	// Second call is a no-op — no disk write, no broadcast. Without this
+	// guard the tray would re-render the menu on every cosmetic re-save of
+	// the preferences file.
+	require.NoError(t, s.SetLanguage("en"))
+	assert.Len(t, emitter.calledWith(EventPreferencesChanged), 1,
+		"re-setting the current language should not broadcast again")
 }
 
 func TestStore_CorruptFileFallsBackToDefault(t *testing.T) {
@@ -173,7 +178,7 @@ func TestStore_CorruptFileFallsBackToDefault(t *testing.T) {
 	require.NoError(t, err, "corrupt file should not fail construction")
 
 	got := s.Get()
-	assert.Equal(t, i18n.DefaultLanguage, got.Language, "corrupt JSON should leave the default in place")
+	assert.Equal(t, i18n.LanguageCode(""), got.Language, "corrupt JSON should leave the empty (unset) default in place so the frontend can re-detect")
 }
 
 func TestStore_UnsubscribeStopsUpdates(t *testing.T) {