diff --git a/packages/app/src/components/reader/TranslationPopover.tsx b/packages/app/src/components/reader/TranslationPopover.tsx
index 1101675e..b424b281 100644
--- a/packages/app/src/components/reader/TranslationPopover.tsx
+++ b/packages/app/src/components/reader/TranslationPopover.tsx
@@ -169,7 +169,7 @@ export function TranslationPopover({ text, position, onClose }: TranslationPopov
   const aiConfig = useSettingsStore((s) => s.aiConfig);
   const endpointId = translationConfig.provider.endpointId || aiConfig.activeEndpointId;
   const endpoint = aiConfig.endpoints.find((e) => e.id === endpointId);
-  const providerName = provider === "ai" ? endpoint?.name || "AI" : "DeepL";
+  const providerName = provider === "ai" ? endpoint?.name || "AI" : translationConfig.provider.name;
 
   return (
     <div
diff --git a/packages/core/src/hooks/useTranslator.ts b/packages/core/src/hooks/useTranslator.ts
index cb9e7933..9ceba14e 100644
--- a/packages/core/src/hooks/useTranslator.ts
+++ b/packages/core/src/hooks/useTranslator.ts
@@ -5,10 +5,10 @@
  */
 
 import { useCallback, useState } from "react";
-import type { AIConfig } from "../types";
 import { useSettingsStore } from "../stores/settings-store";
 import { getFromCache, storeInCache } from "../translation/cache";
-import { aiTranslate, deeplTranslate } from "../translation/providers";
+import { aiTranslate, deeplTranslate, microsoftTranslate } from "../translation/providers";
+import type { AIConfig } from "../types";
 import type { TranslationConfig, TranslationTargetLang } from "../types/translation";
 import { providerRequiresApiKey } from "../utils";
 
@@ -20,7 +20,12 @@ export interface UseTranslatorOptions {
 }
 
 export function useTranslator(options: UseTranslatorOptions = {}) {
-  const { sourceLang = "AUTO", targetLang, aiConfig: aiConfigOverride, translationConfig: translationConfigOverride } = options;
+  const {
+    sourceLang = "AUTO",
+    targetLang,
+    aiConfig: aiConfigOverride,
+    translationConfig: translationConfigOverride,
+  } = options;
   const translationConfigFromStore = useSettingsStore((s) => s.translationConfig);
   const aiConfigFromStore = useSettingsStore((s) => s.aiConfig);
   const translationConfig = translationConfigOverride || translationConfigFromStore;
@@ -92,6 +97,12 @@ export function useTranslator(options: UseTranslatorOptions = {}) {
             apiKey,
             translationConfig.provider.baseUrl,
           );
+        } else if (providerId === "microsoft") {
+          translatedTexts = await microsoftTranslate(
+            needsTranslation.map((n) => n.text),
+            sourceLang,
+            targetLanguage,
+          );
         } else {
           throw new Error(`Unknown translation provider: ${providerId}`);
         }
diff --git a/packages/core/src/translation/providers.test.ts b/packages/core/src/translation/providers.test.ts
index a63e9c1b..ccaf622b 100644
--- a/packages/core/src/translation/providers.test.ts
+++ b/packages/core/src/translation/providers.test.ts
@@ -1,5 +1,9 @@
-import { describe, expect, it } from "vitest";
-import { buildAITranslationPrompt } from "./providers";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { buildAITranslationPrompt, microsoftTranslate, toMicrosoftLangCode } from "./providers";
+
+afterEach(() => {
+  vi.unstubAllGlobals();
+});
 
 describe("buildAITranslationPrompt", () => {
   it("asks AI to translate classical Chinese into modern vernacular Chinese", () => {
@@ -20,3 +24,40 @@ describe("buildAITranslationPrompt", () => {
     expect(prompt).toContain("Do not add any explanation");
   });
 });
+
+describe("Microsoft translator", () => {
+  it("normalizes Chinese language variants to Microsoft script codes", () => {
+    expect(toMicrosoftLangCode("zh-CN")).toBe("zh-Hans");
+    expect(toMicrosoftLangCode("zh-cn")).toBe("zh-Hans");
+    expect(toMicrosoftLangCode("zh_Hans")).toBe("zh-Hans");
+    expect(toMicrosoftLangCode("zh")).toBe("zh-Hans");
+    expect(toMicrosoftLangCode("zh-TW")).toBe("zh-Hant");
+    expect(toMicrosoftLangCode("zh_hant")).toBe("zh-Hant");
+    expect(toMicrosoftLangCode("ja")).toBe("ja");
+  });
+
+  it("requests Simplified Chinese without an empty source language parameter", async () => {
+    const fetchMock = vi
+      .fn()
+      .mockResolvedValueOnce(new Response("token"))
+      .mockResolvedValueOnce(
+        new Response(JSON.stringify([{ translations: [{ text: "你好" }] }]), {
+          headers: { "Content-Type": "application/json" },
+        }),
+      );
+    vi.stubGlobal("fetch", fetchMock);
+
+    await expect(microsoftTranslate(["hello"], "AUTO", "zh_Hans")).resolves.toEqual(["你好"]);
+
+    const [url, init] = fetchMock.mock.calls[1] as [string, RequestInit];
+    const requestUrl = new URL(url);
+    expect(requestUrl.searchParams.get("api-version")).toBe("3.0");
+    expect(requestUrl.searchParams.get("to")).toBe("zh-Hans");
+    expect(requestUrl.searchParams.has("from")).toBe(false);
+    expect(init.headers).toMatchObject({
+      "Content-Type": "application/json",
+      Authorization: "Bearer token",
+    });
+    expect(init.body).toBe(JSON.stringify([{ Text: "hello" }]));
+  });
+});
diff --git a/packages/core/src/translation/providers.ts b/packages/core/src/translation/providers.ts
index 8bfe8a24..26f3a20a 100644
--- a/packages/core/src/translation/providers.ts
+++ b/packages/core/src/translation/providers.ts
@@ -553,12 +553,18 @@ let _msToken: string | null = null;
 let _msTokenExpiry = 0;
 
 /** Language code mapping: our codes → Microsoft API codes */
-function toMicrosoftLangCode(lang: string): string {
-  const map: Record<string, string> = {
-    "zh-CN": "zh-Hans",
-    "zh-TW": "zh-Hant",
-  };
-  return map[lang] || lang;
+export function toMicrosoftLangCode(lang: string): string {
+  const normalized = lang.trim().replace(/_/g, "-");
+  const lower = normalized.toLowerCase();
+
+  if (lower === "zh" || lower === "zh-cn" || lower === "zh-sg" || lower === "zh-hans") {
+    return "zh-Hans";
+  }
+  if (lower === "zh-tw" || lower === "zh-hk" || lower === "zh-mo" || lower === "zh-hant") {
+    return "zh-Hant";
+  }
+
+  return normalized;
 }
 
 /** Microsoft supported source languages (subset for validation) */
@@ -601,11 +607,18 @@ export async function microsoftTranslate(
   // If source lang is "auto"/"AUTO", empty, or not recognized by Microsoft, omit it for auto-detection
   const from = (!sourceLang || sourceLang.toLowerCase() === "auto" || !MS_SUPPORTED_LANGS.has(mappedSource)) ? "" : mappedSource;
   const to = toMicrosoftLangCode(targetLang);
+  const params = new URLSearchParams({
+    "api-version": "3.0",
+    to,
+  });
+  if (from) {
+    params.set("from", from);
+  }
 
   const body = texts.map((t) => ({ Text: t }));
 
   const resp = await fetch(
-    `https://api-edge.cognitive.microsofttranslator.com/translate?from=${from}&to=${to}&api-version=3.0`,
+    `https://api-edge.cognitive.microsofttranslator.com/translate?${params.toString()}`,
     {
       method: "POST",
       headers: {