diff --git a/apps/client/public/locales/en-US/translation.json b/apps/client/public/locales/en-US/translation.json
index fc39a8d9..f1dac8c2 100644
--- a/apps/client/public/locales/en-US/translation.json
+++ b/apps/client/public/locales/en-US/translation.json
@@ -1221,6 +1221,9 @@
   "How transcription requests are sent to the endpoint": "How transcription requests are sent to the endpoint",
   "OpenAI-compatible (multipart/form-data)": "OpenAI-compatible (multipart/form-data)",
   "OpenRouter (JSON, base64 audio)": "OpenRouter (JSON, base64 audio)",
+  "Dictation language": "Dictation language",
+  "Auto-detect": "Auto-detect",
+  "Spoken language hint sent to the transcription model. Auto-detect lets the model decide.": "Spoken language hint sent to the transcription model. Auto-detect lets the model decide.",
   "Agent role": "Agent role",
   "Universal assistant": "Universal assistant",
   "Add role": "Add role",
diff --git a/apps/client/public/locales/ru-RU/translation.json b/apps/client/public/locales/ru-RU/translation.json
index 73a68aa4..6bb76aad 100644
--- a/apps/client/public/locales/ru-RU/translation.json
+++ b/apps/client/public/locales/ru-RU/translation.json
@@ -1123,5 +1123,8 @@
   "Added {{name}} to favorites": "{{name}} добавлено в избранное",
   "Removed {{name}} from favorites": "{{name}} удалено из избранного",
   "Page menu for {{name}}": "Меню страницы для {{name}}",
-  "Create subpage of {{name}}": "Создать подстраницу для {{name}}"
+  "Create subpage of {{name}}": "Создать подстраницу для {{name}}",
+  "Dictation language": "Язык диктовки",
+  "Auto-detect": "Автоопределение",
+  "Spoken language hint sent to the transcription model. Auto-detect lets the model decide.": "Подсказка языка речи для модели транскрипции. «Автоопределение» оставляет выбор за моделью."
 }
diff --git a/apps/client/src/features/workspace/components/settings/components/ai-provider-settings.tsx b/apps/client/src/features/workspace/components/settings/components/ai-provider-settings.tsx
index 4726a0ef..63500797 100644
--- a/apps/client/src/features/workspace/components/settings/components/ai-provider-settings.tsx
+++ b/apps/client/src/features/workspace/components/settings/components/ai-provider-settings.tsx
@@ -42,6 +42,40 @@ import { useAiRolesQuery } from "@/features/ai-chat/queries/ai-chat-query.ts";
 import { IAiRole } from "@/features/ai-chat/types/ai-chat.types.ts";
 import AiMcpServers from "./ai-mcp-servers.tsx";
 
+// Curated ISO-639-1 dictation languages for the STT card. The empty-value
+// "Auto-detect" entry is prepended in render (it needs translation). Values
+// are sent verbatim to the transcription model as the language hint.
+const STT_LANGUAGE_OPTIONS: { value: string; label: string }[] = [
+  { value: "en", label: "English" },
+  { value: "ru", label: "Russian — Русский" },
+  { value: "uk", label: "Ukrainian — Українська" },
+  { value: "de", label: "German — Deutsch" },
+  { value: "fr", label: "French — Français" },
+  { value: "es", label: "Spanish — Español" },
+  { value: "it", label: "Italian — Italiano" },
+  { value: "pt", label: "Portuguese — Português" },
+  { value: "nl", label: "Dutch — Nederlands" },
+  { value: "pl", label: "Polish — Polski" },
+  { value: "tr", label: "Turkish — Türkçe" },
+  { value: "cs", label: "Czech — Čeština" },
+  { value: "sv", label: "Swedish — Svenska" },
+  { value: "fi", label: "Finnish — Suomi" },
+  { value: "da", label: "Danish — Dansk" },
+  { value: "no", label: "Norwegian — Norsk" },
+  { value: "ro", label: "Romanian — Română" },
+  { value: "hu", label: "Hungarian — Magyar" },
+  { value: "el", label: "Greek — Ελληνικά" },
+  { value: "he", label: "Hebrew — עברית" },
+  { value: "ar", label: "Arabic — العربية" },
+  { value: "hi", label: "Hindi — हिन्दी" },
+  { value: "id", label: "Indonesian — Bahasa Indonesia" },
+  { value: "vi", label: "Vietnamese — Tiếng Việt" },
+  { value: "th", label: "Thai — ไทย" },
+  { value: "ja", label: "Japanese — 日本語" },
+  { value: "ko", label: "Korean — 한국어" },
+  { value: "zh", label: "Chinese — 中文" },
+];
+
 // No driver field: every endpoint is OpenAI-compatible, so the form carries only
 // the user-editable fields. `apiKey` / `embeddingApiKey` are write-only buffers
 // (empty means "leave unchanged" unless explicitly cleared).
@@ -63,6 +97,8 @@ const formSchema = z.object({
   sttModel: z.string(),
   sttBaseUrl: z.string(),
   sttApiStyle: z.enum(["multipart", "json"]),
+  // ISO-639-1 dictation language; empty = auto-detect.
+  sttLanguage: z.string(),
   sttApiKey: z.string(),
 });
 
@@ -233,6 +269,7 @@ export default function AiProviderSettings() {
       sttModel: "",
       sttBaseUrl: "",
       sttApiStyle: "multipart" as SttApiStyle,
+      sttLanguage: "",
       sttApiKey: "",
     },
   });
@@ -254,6 +291,7 @@ export default function AiProviderSettings() {
       sttModel: settings.sttModel ?? "",
       sttBaseUrl: settings.sttBaseUrl ?? "",
       sttApiStyle: settings.sttApiStyle ?? "multipart",
+      sttLanguage: settings.sttLanguage ?? "",
       sttApiKey: "",
     });
     form.resetDirty();
@@ -288,6 +326,7 @@ export default function AiProviderSettings() {
       sttModel: values.sttModel,
       sttBaseUrl: values.sttBaseUrl,
       sttApiStyle: values.sttApiStyle,
+      sttLanguage: values.sttLanguage,
     };
 
     // Key semantics (never send the stored key back) — see resolveKeyField:
@@ -923,6 +962,22 @@ export default function AiProviderSettings() {
           {...form.getInputProps("sttApiStyle")}
         />
 
+        <Select
+          mt="sm"
+          label={t("Dictation language")}
+          description={t(
+            "Spoken language hint sent to the transcription model. Auto-detect lets the model decide.",
+          )}
+          data={[
+            { value: "", label: t("Auto-detect") },
+            ...STT_LANGUAGE_OPTIONS,
+          ]}
+          searchable
+          allowDeselect={false}
+          disabled={isLoading}
+          {...form.getInputProps("sttLanguage")}
+        />
+
         <TextInput
           mt="sm"
           label={t("Base URL")}
diff --git a/apps/client/src/features/workspace/services/ai-settings-service.ts b/apps/client/src/features/workspace/services/ai-settings-service.ts
index 36468b04..1814acd5 100644
--- a/apps/client/src/features/workspace/services/ai-settings-service.ts
+++ b/apps/client/src/features/workspace/services/ai-settings-service.ts
@@ -33,6 +33,8 @@ export interface IAiSettings {
   sttModel?: string;
   sttBaseUrl?: string;
   sttApiStyle?: SttApiStyle;
+  // ISO-639-1 dictation language; empty = auto-detect.
+  sttLanguage?: string;
   hasSttApiKey: boolean;
   // RAG indexing coverage (pages indexed for semantic search).
   indexedPages: number;
@@ -60,6 +62,8 @@ export interface IAiSettingsUpdate {
   sttModel?: string;
   sttBaseUrl?: string;
   sttApiStyle?: SttApiStyle;
+  // ISO-639-1 dictation language; empty = auto-detect.
+  sttLanguage?: string;
   // Write-only STT key (same semantics as `apiKey` / `embeddingApiKey`).
   sttApiKey?: string;
 }
diff --git a/apps/server/src/database/repos/workspace/workspace.repo.ts b/apps/server/src/database/repos/workspace/workspace.repo.ts
index ff45df3e..182a45f2 100644
--- a/apps/server/src/database/repos/workspace/workspace.repo.ts
+++ b/apps/server/src/database/repos/workspace/workspace.repo.ts
@@ -239,7 +239,7 @@ export class WorkspaceRepo {
     // is a real jsonb object, never a double-encoded string. The CASE self-heals
     // workspaces whose settings.ai.provider was previously corrupted into an
     // array/string.
-    const ALLOWED = ['driver', 'chatModel', 'embeddingModel', 'baseUrl', 'embeddingBaseUrl', 'sttModel', 'sttBaseUrl', 'sttApiStyle', 'systemPrompt', 'publicShareChatModel', 'publicShareAssistantRoleId'];
+    const ALLOWED = ['driver', 'chatModel', 'embeddingModel', 'baseUrl', 'embeddingBaseUrl', 'sttModel', 'sttBaseUrl', 'sttApiStyle', 'sttLanguage', 'systemPrompt', 'publicShareChatModel', 'publicShareAssistantRoleId'];
     const entries = Object.entries(provider).filter(
       ([k, v]) => v !== undefined && ALLOWED.includes(k),
     );
diff --git a/apps/server/src/integrations/ai/ai-settings.service.ts b/apps/server/src/integrations/ai/ai-settings.service.ts
index 6dafe127..e556c0d0 100644
--- a/apps/server/src/integrations/ai/ai-settings.service.ts
+++ b/apps/server/src/integrations/ai/ai-settings.service.ts
@@ -33,6 +33,8 @@ export interface UpdateAiSettingsInput {
   sttModel?: string;
   sttBaseUrl?: string;
   sttApiStyle?: SttApiStyle;
+  // ISO-639-1 dictation language hint (e.g. 'en', 'ru'). Empty = auto-detect.
+  sttLanguage?: string;
   sttApiKey?: string;
   publicShareChatModel?: string;
   publicShareAssistantRoleId?: string;
@@ -166,6 +168,8 @@ export class AiSettingsService {
       // Plain passthrough, no fallback; the transcribe path defaults unset to
       // 'multipart' (current behavior).
       sttApiStyle: provider.sttApiStyle,
+      // Plain passthrough; empty/unset = auto-detect at the transcribe path.
+      sttLanguage: provider.sttLanguage,
       baseUrl: provider.baseUrl,
       systemPrompt: provider.systemPrompt,
     };
@@ -240,6 +244,7 @@ export class AiSettingsService {
       sttModel: provider.sttModel,
       sttBaseUrl: provider.sttBaseUrl,
       sttApiStyle: provider.sttApiStyle,
+      sttLanguage: provider.sttLanguage,
       systemPrompt: provider.systemPrompt,
       publicShareChatModel: provider.publicShareChatModel,
       publicShareAssistantRoleId: provider.publicShareAssistantRoleId,
@@ -279,6 +284,7 @@ export class AiSettingsService {
       'sttModel',
       'sttBaseUrl',
       'sttApiStyle',
+      'sttLanguage',
       'systemPrompt',
       'publicShareChatModel',
       'publicShareAssistantRoleId',
diff --git a/apps/server/src/integrations/ai/ai.service.ts b/apps/server/src/integrations/ai/ai.service.ts
index f6593f4c..858118f0 100644
--- a/apps/server/src/integrations/ai/ai.service.ts
+++ b/apps/server/src/integrations/ai/ai.service.ts
@@ -212,12 +212,22 @@ export class AiService {
     const cfg = await this.aiSettings.resolve(workspaceId);
     if (!cfg?.sttModel) throw new AiSttNotConfiguredException();
     const baseURL = cfg.sttBaseUrl || cfg.baseUrl;
+    // Trimmed language hint; empty/unset = auto-detect (never forward an empty
+    // string to the provider, which would override auto-detect).
+    const sttLanguage = cfg.sttLanguage?.trim() || undefined;
 
     // Explicit, admin-chosen request encoding (no URL guessing). 'json' is the
     // OpenRouter style (JSON + base64 input_audio); everything else uses the
     // OpenAI-compatible multipart path via the AI SDK.
     if (cfg.sttApiStyle === 'json') {
-      return this.transcribeJsonBase64(baseURL, cfg.sttApiKey, cfg.sttModel, audio, format);
+      return this.transcribeJsonBase64(
+        baseURL,
+        cfg.sttApiKey,
+        cfg.sttModel,
+        audio,
+        format,
+        sttLanguage,
+      );
     }
 
     // Standard OpenAI-compatible multipart path (AI SDK). apiKey may be unused for
@@ -226,14 +236,23 @@ export class AiService {
       apiKey: cfg.sttApiKey ?? 'unused',
       baseURL,
     }).transcription(cfg.sttModel);
-    const { text } = await transcribe({ model, audio });
+    const { text } = await transcribe({
+      model,
+      audio,
+      // Forward the language hint only when set; the OpenAI transcription model
+      // reads it from providerOptions.openai.language.
+      ...(sttLanguage
+        ? { providerOptions: { openai: { language: sttLanguage } } }
+        : {}),
+    });
     return text.trim();
   }
 
   /**
    * JSON + base64 transcription body (OpenRouter-style). POSTs
    * { model, input_audio: { data, format } } to {baseURL}/audio/transcriptions
-   * and returns { text }.
+   * and returns { text }. The optional `language` ISO-639-1 hint is included as
+   * a top-level body field only when set (empty/unset = auto-detect).
    */
   private async transcribeJsonBase64(
     baseURL: string | undefined,
@@ -241,6 +260,7 @@ export class AiService {
     model: string,
     audio: Uint8Array,
     format: string,
+    language?: string,
   ): Promise<string> {
     if (!baseURL) {
       throw new BadRequestException(
@@ -256,6 +276,7 @@ export class AiService {
       },
       body: JSON.stringify({
         model,
+        ...(language ? { language } : {}),
         input_audio: {
           data: Buffer.from(audio).toString('base64'),
           format,
diff --git a/apps/server/src/integrations/ai/ai.types.ts b/apps/server/src/integrations/ai/ai.types.ts
index d6a70892..0a3d925e 100644
--- a/apps/server/src/integrations/ai/ai.types.ts
+++ b/apps/server/src/integrations/ai/ai.types.ts
@@ -31,6 +31,8 @@ export interface AiProviderSettings {
   // STT-specific base URL. Falls back to baseUrl when empty/unset.
   sttBaseUrl?: string;
   sttApiStyle?: SttApiStyle;
+  // ISO-639-1 dictation language hint (e.g. 'en', 'ru'). Empty/unset = auto-detect.
+  sttLanguage?: string;
   systemPrompt?: string;
   // Cheap chat model id used ONLY by the anonymous public-share assistant. The
   // driver / baseUrl / apiKey of the main chat provider are reused; this is the
@@ -80,6 +82,8 @@ export interface MaskedAiSettings {
   sttModel?: string;
   sttBaseUrl?: string;
   sttApiStyle?: SttApiStyle;
+  // ISO-639-1 dictation language hint (e.g. 'en', 'ru'). Empty/unset = auto-detect.
+  sttLanguage?: string;
   systemPrompt?: string;
   publicShareChatModel?: string;
   // Agent-role id whose persona the public-share assistant adopts; empty/unset
diff --git a/apps/server/src/integrations/ai/dto/update-ai-settings.dto.ts b/apps/server/src/integrations/ai/dto/update-ai-settings.dto.ts
index 891304ce..37fe8143 100644
--- a/apps/server/src/integrations/ai/dto/update-ai-settings.dto.ts
+++ b/apps/server/src/integrations/ai/dto/update-ai-settings.dto.ts
@@ -54,6 +54,11 @@ export class UpdateAiSettingsDto {
   @IsIn(STT_API_STYLES)
   sttApiStyle?: SttApiStyle;
 
+  // ISO-639-1 dictation language hint (e.g. 'en', 'ru'). Empty = auto-detect.
+  @IsOptional()
+  @IsString()
+  sttLanguage?: string;
+
   @IsOptional()
   @IsString()
   sttApiKey?: string;