fix: allow specifying transcription language

docs/configuration.md

@@ -45,7 +45,7 @@ IMAP_PASSWORD=your-password-here
 ## Providers
 
 > [!TIP]
-> - **Voice transcription**: Voice messages (Telegram, WhatsApp) are automatically transcribed using Whisper. By default Groq is used (free tier). Set `"transcriptionProvider": "openai"` under `channels` to use OpenAI Whisper instead — the API key is picked from the matching provider config.
+> - **Voice transcription**: Voice messages (Telegram, WhatsApp) are automatically transcribed using Whisper. By default Groq is used (free tier). Set `"transcriptionProvider": "openai"` under `channels` to use OpenAI Whisper instead, and optionally set `"transcriptionLanguage": "en"` (or another ISO-639-1 code) for more accurate transcription. The API key is picked from the matching provider config.
 > - **MiniMax Coding Plan**: Exclusive discount links for the nanobot community: [Overseas](https://platform.minimax.io/subscribe/coding-plan?code=9txpdXw04g&source=link) · [Mainland China](https://platform.minimaxi.com/subscribe/token-plan?code=GILTJpMTqZ&source=link)
 > - **MiniMax (Mainland China)**: If your API key is from MiniMax's mainland China platform (minimaxi.com), set `"apiBase": "https://api.minimaxi.com/v1"` in your minimax provider config.
 > - **MiniMax thinking mode**: Use `providers.minimaxAnthropic` when you want `reasoningEffort` / thinking mode. MiniMax exposes that capability through its Anthropic-compatible endpoint, so nanobot keeps it as a separate provider instead of guessing MiniMax-specific thinking parameters on the generic OpenAI-compatible `minimax` endpoint. It uses the same `MINIMAX_API_KEY`. Default Anthropic-compatible base URL: `https://api.minimax.io/anthropic`; for mainland China use `https://api.minimaxi.com/anthropic`.
@@ -440,6 +440,7 @@ Global settings that apply to all channels. Configure under the `channels` secti
     "sendToolHints": false,
     "sendMaxRetries": 3,
     "transcriptionProvider": "groq",
+    "transcriptionLanguage": null,
     "telegram": { ... }
   }
 }
@@ -451,6 +452,7 @@ Global settings that apply to all channels. Configure under the `channels` secti
 | `sendToolHints` | `false` | Stream tool-call hints (e.g. `read_file("…")`) |
 | `sendMaxRetries` | `3` | Max delivery attempts per outbound message, including the initial send (0-10 configured, minimum 1 actual attempt) |
 | `transcriptionProvider` | `"groq"` | Voice transcription backend: `"groq"` (free tier, default) or `"openai"`. API key is auto-resolved from the matching provider config. |
+| `transcriptionLanguage` | `null` | Optional ISO-639-1 language hint for audio transcription, e.g. `"en"`, `"ko"`, `"ja"`. |
 
 ### Retry Behavior