diff --git a/apps/desktop/src/features/settings/CommitSettingsCard.tsx b/apps/desktop/src/features/settings/CommitSettingsCard.tsx
index e52d3a0..29bc3b2 100644
--- a/apps/desktop/src/features/settings/CommitSettingsCard.tsx
+++ b/apps/desktop/src/features/settings/CommitSettingsCard.tsx
@@ -1,5 +1,6 @@
 import { useCallback, useEffect, useMemo, useState } from "react";
 import { api, pluginText, type CommitSettingsView } from "../../shared/api";
+import { commitPromptLocale } from "../../i18n/runtime";
 import { useI18n } from "../../i18n/store";
 import { useAppStore } from "../../shared/store/appStore";
 import { Button } from "../../shared/ui/Button";
@@ -33,11 +34,12 @@ export function CommitSettingsCard() {
     void (async () => {
       try {
         let loaded = await api.commitSettings(locale);
-        if (!loaded.prompt.trim() && loaded.prompt_locale !== locale) {
+        const promptLocale = commitPromptLocale(locale);
+        if (!loaded.prompt.trim() && loaded.prompt_locale !== promptLocale) {
           loaded = await api.setCommitSettings({
             model_id: loaded.model_id,
             prompt: "",
-            prompt_locale: locale,
+            prompt_locale: promptLocale,
           });
         }
         if (active) {
@@ -97,7 +99,7 @@ export function CommitSettingsCard() {
       return api.setCommitSettings({
         model_id: modelId,
         prompt: normalizedPrompt,
-        prompt_locale: locale,
+        prompt_locale: commitPromptLocale(locale),
       });
     },
     [view, locale],
diff --git a/apps/desktop/src/i18n/runtime.ts b/apps/desktop/src/i18n/runtime.ts
index 98a458c..89c71b1 100644
--- a/apps/desktop/src/i18n/runtime.ts
+++ b/apps/desktop/src/i18n/runtime.ts
@@ -3,6 +3,12 @@ import enUS from "./locales/en-US.json";
 import ptBR from "./locales/pt-BR.json";
 
 export type Locale = "zh-CN" | "en-US" | "pt-BR";
+export type CommitPromptLocale = "zh-CN" | "en-US";
+
+export function commitPromptLocale(locale: Locale): CommitPromptLocale {
+  return locale === "zh-CN" ? "zh-CN" : "en-US";
+}
+
 export type TranslationValue = string | number;
 export type TranslationParams = Readonly<Record<string, TranslationValue>>;
 
diff --git a/apps/desktop/src/shared/api.ts b/apps/desktop/src/shared/api.ts
index 5882a10..2642f2e 100644
--- a/apps/desktop/src/shared/api.ts
+++ b/apps/desktop/src/shared/api.ts
@@ -1,5 +1,5 @@
 import type { AdRuntime } from "../shell/ads/types";
-import type { Locale } from "../i18n/runtime";
+import type { CommitPromptLocale, Locale } from "../i18n/runtime";
 
 export type ModelType = "openai" | "anthropic";
 
@@ -154,7 +154,7 @@ export interface DesktopSettings {
 export interface CommitSettings {
   model_id: string;
   prompt: string;
-  prompt_locale: Locale;
+  prompt_locale: CommitPromptLocale;
 }
 
 export interface CommitSettingsView extends CommitSettings {
diff --git a/server/src/control/settings.rs b/server/src/control/settings.rs
index 9ade848..003c1c9 100644
--- a/server/src/control/settings.rs
+++ b/server/src/control/settings.rs
@@ -149,13 +149,11 @@ pub async fn update_pricing_settings(
 }
 
 fn requested_commit_locale(headers: &HeaderMap) -> CommitPromptLocale {
-    match headers
+    headers
         .get(header::ACCEPT_LANGUAGE)
         .and_then(|value| value.to_str().ok())
-    {
-        Some(value) if value.eq_ignore_ascii_case("zh-CN") => CommitPromptLocale::ZhCn,
-        _ => CommitPromptLocale::EnUs,
-    }
+        .map(CommitPromptLocale::from_interface_language)
+        .unwrap_or(CommitPromptLocale::EnUs)
 }
 
 #[cfg(test)]
@@ -170,5 +168,8 @@ mod tests {
 
         headers.insert(header::ACCEPT_LANGUAGE, "en-US".parse().unwrap());
         assert_eq!(requested_commit_locale(&headers), CommitPromptLocale::EnUs);
+
+        headers.insert(header::ACCEPT_LANGUAGE, "pt-BR".parse().unwrap());
+        assert_eq!(requested_commit_locale(&headers), CommitPromptLocale::EnUs);
     }
 }
diff --git a/server/src/store/settings.rs b/server/src/store/settings.rs
index 2f842c3..1a2673c 100644
--- a/server/src/store/settings.rs
+++ b/server/src/store/settings.rs
@@ -1,5 +1,5 @@
 //! Persists application settings.
-use serde::{Deserialize, Serialize};
+use serde::{Deserialize, Deserializer, Serialize};
 
 use crate::Result;
 
@@ -105,7 +105,7 @@ impl TabSettings {
     }
 }
 
-#[derive(Clone, Copy, Debug, Default, Deserialize, PartialEq, Eq, Serialize)]
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Serialize)]
 pub enum CommitPromptLocale {
     #[default]
     #[serde(rename = "zh-CN")]
@@ -115,6 +115,14 @@ pub enum CommitPromptLocale {
 }
 
 impl CommitPromptLocale {
+    pub fn from_interface_language(value: &str) -> Self {
+        if value.eq_ignore_ascii_case("zh-CN") {
+            Self::ZhCn
+        } else {
+            Self::EnUs
+        }
+    }
+
     pub fn default_prompt(self) -> &'static str {
         match self {
             Self::ZhCn => DEFAULT_COMMIT_PROMPT_ZH_CN.trim(),
@@ -123,6 +131,13 @@ impl CommitPromptLocale {
     }
 }
 
+impl<'de> Deserialize<'de> for CommitPromptLocale {
+    fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
+        let value = String::deserialize(deserializer)?;
+        Ok(Self::from_interface_language(&value))
+    }
+}
+
 /// User preferences for Git commit message generation.
 ///
 /// Empty `model_id` means 直连: forward the original Cursor RPC unchanged.
@@ -490,6 +505,26 @@ mod tests {
     const LEGACY_PROXY_ROW: &str =
         r#"{"mode":"system","address":"","auth_enabled":false,"username":"","password":""}"#;
 
+    #[test]
+    fn commit_prompt_locale_maps_unknown_interface_languages_to_english() {
+        assert_eq!(
+            serde_json::from_str::<CommitPromptLocale>(r#""zh-CN""#).unwrap(),
+            CommitPromptLocale::ZhCn
+        );
+        assert_eq!(
+            serde_json::from_str::<CommitPromptLocale>(r#""en-US""#).unwrap(),
+            CommitPromptLocale::EnUs
+        );
+        assert_eq!(
+            serde_json::from_str::<CommitPromptLocale>(r#""pt-BR""#).unwrap(),
+            CommitPromptLocale::EnUs
+        );
+        assert_eq!(
+            serde_json::to_string(&CommitPromptLocale::EnUs).unwrap(),
+            r#""en-US""#
+        );
+    }
+
     #[test]
     fn default_commit_prompt_follows_its_saved_locale() {
         for (prompt_locale, expected) in [