feat(coach): mehrsprachiges TTS — locale durchreichen + Cartesia Sonic-3

TTS-Sprache war provider-übergreifend hart auf "de" verdrahtet, locale aus dem
Request wurde ignoriert → arabischer Text wurde deutsch-phonetisch gesprochen.

- locale aus Body auslesen → Basis-Sprachcode an alle Provider
- Pro: Cartesia sonic-2 → sonic-3 (sonic-2 kann kein Arabisch; sonic-3 = 42 Sprachen)
- Legend: ElevenLabs language_code gesetzt (turbo_v2_5 multilingual, ar dabei)
- Google-Fallback: BCP-47-Map (ar→ar-XA etc.), de-Voice nur noch für de

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/server/api/coach/speak.post.ts

@@ -31,9 +31,10 @@ export default defineEventHandler(async (event) => {
   const user = await requireUser(event);
 
   const body = await readBody(event);
-  const { text, mode } = body as {
+  const { text, mode, locale } = body as {
     text?: string;
     mode?: "chat" | "sos" | "sos-continuation";
+    locale?: string;
   };
 
   if (!text?.trim()) {
@@ -41,6 +42,9 @@ export default defineEventHandler(async (event) => {
   }
 
   const trimmed = text.slice(0, 4096);
+  // i18n-Locale (z.B. "ar", "de-DE") → 2-Buchstaben-Basis-Sprachcode für die
+  // Provider. Ohne das sprach Lyra arabischen Text mit deutscher Stimme/Phonetik.
+  const lang = (locale ?? "de").split("-")[0].toLowerCase();
 
   // ─── Load profile + plan ────────────────────────────────────────────────
   const db = usePrisma();
@@ -76,15 +80,15 @@ export default defineEventHandler(async (event) => {
   // ─── Dispatch per provider ───────────────────────────────────────────────
   switch (voiceCfg.provider) {
     case "google":
-      return await speakGoogle(event, trimmed, config, voiceCfg, user.id, plan);
+      return await speakGoogle(event, trimmed, config, voiceCfg, user.id, plan, lang);
     case "cartesia":
-      return await speakCartesia(event, trimmed, config, voiceCfg, user.id, plan);
+      return await speakCartesia(event, trimmed, config, voiceCfg, user.id, plan, lang);
     case "elevenlabs":
-      return await speakElevenLabs(event, trimmed, mode, config, voiceCfg, user.id, plan, userLyraVoiceId);
+      return await speakElevenLabs(event, trimmed, mode, config, voiceCfg, user.id, plan, userLyraVoiceId, lang);
     default: {
       // Unknown provider in config — fallback to Google with warning
       console.warn("[speak] unknown provider in plan-features:", voiceCfg.provider, "→ falling back to google");
-      return await speakGoogle(event, trimmed, config, voiceCfg, user.id, plan);
+      return await speakGoogle(event, trimmed, config, voiceCfg, user.id, plan, lang);
     }
   }
 });
@@ -98,13 +102,23 @@ async function speakGoogle(
   voiceCfg: VoiceConfig,
   userId: string,
   plan: string,
+  lang: string,
 ) {
   const key = (config.googleApiKey as string) || process.env.GOOGLE_API_KEY || "";
   if (!key) {
     throw createError({ statusCode: 503, message: "Google TTS API Key nicht konfiguriert" });
   }
 
-  const voiceName = voiceCfg.model ?? "de-DE-Neural2-F";
+  // Google-Stimmen sind sprachgebunden — eine de-DE-Stimme kann kein Arabisch.
+  // BCP-47-LanguageCode aus dem Basis-Locale ableiten; den konfigurierten
+  // Voice-Namen nur für Deutsch verwenden, sonst Google eine Default-Stimme
+  // der Zielsprache wählen lassen (name weglassen + ssmlGender).
+  const GOOGLE_LANG: Record<string, string> = {
+    de: "de-DE", en: "en-US", fr: "fr-FR", ar: "ar-XA",
+    tr: "tr-TR", es: "es-ES", pt: "pt-PT", it: "it-IT",
+  };
+  const languageCode = GOOGLE_LANG[lang] ?? "de-DE";
+  const voiceName = lang === "de" ? (voiceCfg.model ?? "de-DE-Neural2-F") : undefined;
 
   const response = await fetch(
     `https://texttospeech.googleapis.com/v1/text:synthesize?key=${key}`,
@@ -114,8 +128,8 @@ async function speakGoogle(
       body: JSON.stringify({
         input: { text },
         voice: {
-          languageCode: "de-DE",
+          languageCode,
-          name: voiceName,
+          ...(voiceName ? { name: voiceName } : {}),
           ssmlGender: "FEMALE",
         },
         audioConfig: {
@@ -157,6 +171,7 @@ async function speakCartesia(
   voiceCfg: VoiceConfig,
   userId: string,
   plan: string,
+  lang: string,
 ) {
   const key = (config.cartesiaApiKey as string) || process.env.CARTESIA_API_KEY || "";
   if (!key) {
@@ -178,7 +193,7 @@ async function speakCartesia(
       "Content-Type": "application/json",
     },
     body: JSON.stringify({
-      model_id: voiceCfg.model ?? "sonic-2",
+      model_id: voiceCfg.model ?? "sonic-3",
       transcript: text,
       voice: { mode: "id", id: voiceId },
       output_format: {
@@ -186,7 +201,9 @@ async function speakCartesia(
         sample_rate: 22050,
         bit_rate: 64000,
       },
-      language: "de",
+      // Sonic-3 unterstützt 42 Sprachen inkl. ar — language aus User-Locale
+      // statt hardcoded "de", sonst klingt arabischer Text deutsch-phonetisch.
+      language: lang,
     }),
   });
 
@@ -214,6 +231,7 @@ async function speakElevenLabs(
   userId: string,
   plan: string,
   userLyraVoiceId: string | null = null,
+  lang: string = "de",
 ) {
   const key =
     (config.elevenlabsApiKey as string) || process.env.ELEVENLABS_API_KEY || "";
@@ -244,6 +262,10 @@ async function speakElevenLabs(
       body: JSON.stringify({
         text,
         model_id: modelId,
+        // Turbo v2.5 ist multilingual (32 Sprachen inkl. ar) — dieselbe Stimme
+        // spricht die Zielsprache. language_code explizit setzen statt nur
+        // Auto-Detect, damit kurze Texte zuverlässig in der User-Sprache landen.
+        language_code: lang,
         voice_settings: {
           stability: 0.5,
           similarity_boost: 0.75,

backend/server/utils/plan-features.ts

@@ -98,7 +98,7 @@ export const PLAN_LIMITS: Record<Exclude<Plan, "free">, PlanLimits> = {
     aiProvider: "groq",
     voice: {
       provider: "cartesia",
-      model: "sonic-2",         // Cartesia Sonic-2 — ~75ms TTFT, native German, ~$4/1M chars
+      model: "sonic-3",         // Cartesia Sonic-3 — 42 Sprachen inkl. Arabisch (sonic-2 konnte nur 15, kein ar)
       dailyQuotaSeconds: 300,   // 5 Minuten/Tag
     },
   },