diff --git a/src/media-understanding/openai-compatible-audio.test.ts b/src/media-understanding/openai-compatible-audio.test.ts
index fa39a2d4c7a7..1989c9e98c2b 100644
--- a/src/media-understanding/openai-compatible-audio.test.ts
+++ b/src/media-understanding/openai-compatible-audio.test.ts
@@ -75,6 +75,29 @@ describe("transcribeOpenAiCompatibleAudio", () => {
     expect((file as File).name).toBe("voice-note.m4a");
   });
 
+  it("omits the optional prompt field while preserving language hints", async () => {
+    const { fetchFn, getRequest } = createRequestCaptureJsonFetch({ text: "ok" });
+
+    await transcribeOpenAiCompatibleAudio({
+      buffer: Buffer.from("audio"),
+      fileName: "note.ogg",
+      mime: "audio/ogg",
+      apiKey: "test-key",
+      timeoutMs: 1000,
+      fetchFn,
+      provider: "groq",
+      baseUrl: "https://api.groq.com/openai/v1",
+      defaultBaseUrl: "https://api.groq.com/openai/v1",
+      defaultModel: "whisper-large-v3-turbo",
+      language: "ru",
+    });
+
+    const form = getRequest().init?.body;
+    expect(form).toBeInstanceOf(FormData);
+    expect((form as FormData).get("language")).toBe("ru");
+    expect((form as FormData).get("prompt")).toBeNull();
+  });
+
   it("omits bearer auth for explicit no-auth requests", async () => {
     const { fetchFn, getRequest } = createRequestCaptureJsonFetch({ text: "ok" });
 
diff --git a/src/media-understanding/runner.auto-audio.test.ts b/src/media-understanding/runner.auto-audio.test.ts
index 0dae19d77a96..452fb66962cf 100644
--- a/src/media-understanding/runner.auto-audio.test.ts
+++ b/src/media-understanding/runner.auto-audio.test.ts
@@ -5,6 +5,7 @@ import os from "node:os";
 import path from "node:path";
 import { describe, expect, it, vi } from "vitest";
 import type { OpenClawConfig } from "../config/types.js";
+import type { MediaUnderstandingConfig } from "../config/types.tools.js";
 import { withEnvAsync } from "../test-utils/env.js";
 import { clearMediaUnderstandingBinaryCacheForTests, runCapability } from "./runner.js";
 import { withAudioFixture } from "./runner.test-utils.js";
@@ -400,6 +401,78 @@ describe("runCapability auto audio entries", () => {
     expect(seenPrompt).toBe("Focus on names");
   });
 
+  it("omits the implicit English audio prompt when a non-English language is configured", async () => {
+    let seenLanguage: string | undefined;
+    let seenPrompt: string | undefined;
+    const result = await runAutoAudioCase({
+      transcribeAudio: async (req) => {
+        seenLanguage = req.language;
+        seenPrompt = req.prompt;
+        return { text: "ok", model: req.model ?? "unknown" };
+      },
+      cfgExtra: {
+        tools: {
+          media: {
+            audio: {
+              enabled: true,
+              language: "ru",
+              models: [{ provider: "openai", model: "whisper-1" }],
+            },
+          },
+        },
+      } as Partial<OpenClawConfig>,
+    });
+
+    expect(requireCapabilityOutput(result, 0).text).toBe("ok");
+    expect(seenLanguage).toBe("ru");
+    expect(seenPrompt).toBeUndefined();
+  });
+
+  it("keeps explicit and English-compatible audio prompts", async () => {
+    const seenPrompts: Array<string | undefined> = [];
+    const runCase = async (audio: MediaUnderstandingConfig) => {
+      await runAutoAudioCase({
+        transcribeAudio: async (req) => {
+          seenPrompts.push(req.prompt);
+          return { text: "ok", model: req.model ?? "unknown" };
+        },
+        cfgExtra: {
+          tools: {
+            media: {
+              audio,
+            },
+          },
+        } as Partial<OpenClawConfig>,
+      });
+    };
+
+    await runCase({
+      enabled: true,
+      language: "ru",
+      prompt: "Transcribe in Russian.",
+      models: [{ provider: "openai", model: "whisper-1" }],
+    });
+    for (const language of ["en-US", "eng", "english"]) {
+      await runCase({
+        enabled: true,
+        language,
+        models: [{ provider: "openai", model: "whisper-1" }],
+      });
+    }
+    await runCase({
+      enabled: true,
+      models: [{ provider: "openai", model: "whisper-1" }],
+    });
+
+    expect(seenPrompts).toEqual([
+      "Transcribe in Russian.",
+      "Transcribe the audio.",
+      "Transcribe the audio.",
+      "Transcribe the audio.",
+      "Transcribe the audio.",
+    ]);
+  });
+
   it("uses mistral when only mistral key is configured", async () => {
     const isolatedAgentDir = await fs.mkdtemp(path.join(os.tmpdir(), "openclaw-audio-agent-"));
     let runResult: Awaited<ReturnType<typeof runCapability>> | undefined;
diff --git a/src/media-understanding/runner.entries.ts b/src/media-understanding/runner.entries.ts
index fd0f4b3e8eb3..dab99aa7cf09 100644
--- a/src/media-understanding/runner.entries.ts
+++ b/src/media-understanding/runner.entries.ts
@@ -397,7 +397,13 @@ function resolveEntryRunOptions(params: {
   entry: MediaUnderstandingModelConfig;
   cfg: OpenClawConfig;
   config?: MediaUnderstandingConfig;
-}): { maxBytes: number; maxChars?: number; timeoutMs: number; prompt: string } {
+}): {
+  maxBytes: number;
+  maxChars?: number;
+  timeoutMs: number;
+  prompt: string;
+  hasConfiguredPrompt: boolean;
+} {
   const { capability, entry, cfg } = params;
   const maxBytes = resolveMaxBytes({ capability, entry, cfg, config: params.config });
   const maxChars = resolveMaxChars({ capability, entry, cfg, config: params.config });
@@ -407,12 +413,16 @@ function resolveEntryRunOptions(params: {
       cfg.tools?.media?.[capability]?.timeoutSeconds,
     DEFAULT_TIMEOUT_SECONDS[capability],
   );
-  const prompt = resolvePrompt(
-    capability,
-    entry.prompt ?? params.config?.prompt ?? cfg.tools?.media?.[capability]?.prompt,
+  const configuredPrompt =
+    entry.prompt ?? params.config?.prompt ?? cfg.tools?.media?.[capability]?.prompt;
+  const prompt = resolvePrompt(capability, configuredPrompt, maxChars);
+  return {
+    maxBytes,
     maxChars,
-  );
-  return { maxBytes, maxChars, timeoutMs, prompt };
+    timeoutMs,
+    prompt,
+    hasConfiguredPrompt: Boolean(configuredPrompt?.trim()),
+  };
 }
 
 function resolveMediaRequestOverrides(config: MediaUnderstandingConfig | undefined): {
@@ -429,6 +439,28 @@ function resolveMediaRequestOverrides(config: MediaUnderstandingConfig | undefin
   };
 }
 
+function resolveAudioProviderPrompt(params: {
+  prompt: string;
+  hasConfiguredPrompt: boolean;
+  language?: string;
+}): string | undefined {
+  const language = params.language?.trim().toLowerCase();
+  const isEnglish =
+    !language ||
+    language === "en" ||
+    language === "eng" ||
+    language === "english" ||
+    language.startsWith("en-") ||
+    language.startsWith("en_");
+  if (params.hasConfiguredPrompt || isEnglish) {
+    return params.prompt;
+  }
+  // OpenAI-compatible transcription prompts guide style/context and should
+  // match the audio language; omit OpenClaw's English default for non-English
+  // language hints unless the user supplied an explicit prompt.
+  return undefined;
+}
+
 type ProviderExecutionAuth =
   | {
       kind: "api-key";
@@ -727,7 +759,7 @@ export async function runProviderEntry(params: {
   }
   const providerId = normalizeMediaProviderId(providerIdRaw);
   const requestProviderId = normalizeMediaExecutionProviderId(providerIdRaw);
-  const { maxBytes, maxChars, timeoutMs, prompt } = resolveEntryRunOptions({
+  const { maxBytes, maxChars, timeoutMs, prompt, hasConfiguredPrompt } = resolveEntryRunOptions({
     capability,
     entry,
     cfg,
@@ -803,6 +835,18 @@ export async function runProviderEntry(params: {
       timeoutMs,
     });
     assertMinAudioSize({ size: media.size, attachmentIndex: params.attachmentIndex });
+    const audioLanguage =
+      requestOverrides.language ??
+      entry.language ??
+      params.config?.language ??
+      cfg.tools?.media?.audio?.language;
+    const audioPrompt =
+      requestOverrides.prompt ??
+      resolveAudioProviderPrompt({
+        prompt,
+        hasConfiguredPrompt,
+        language: audioLanguage,
+      });
     const { auth, baseUrl, headers, request } = await resolveProviderExecutionContext({
       capability,
       providerId,
@@ -841,12 +885,8 @@ export async function runProviderEntry(params: {
       headers,
       request,
       model,
-      language:
-        requestOverrides.language ??
-        entry.language ??
-        params.config?.language ??
-        cfg.tools?.media?.audio?.language,
-      prompt: requestOverrides.prompt ?? prompt,
+      language: audioLanguage,
+      prompt: audioPrompt,
       query: providerQuery,
       timeoutMs,
       fetchFn,