feat: add system language detection and prompt on first launch

src/localization/index.js

@@ -4,29 +4,25 @@ const localizedStringsUrls = import.meta.glob('./*.json', {
     import: 'default'
 });
 
-async function fetchJson(url) {
-    const response = await fetch(url);
-    if (!response.ok) {
-        console.warn(`Failed to fetch localization: ${response.status}`);
-    }
-    return response.json();
-}
-
 async function getLocalizedStrings(code) {
     const fallbackUrl = localizedStringsUrls['./en.json'];
-    const localizedStringsUrl =
-        localizedStringsUrls[`./${code}.json`] || fallbackUrl;
+    const url = localizedStringsUrls[`./${code}.json`] || fallbackUrl;
 
-    let localizedStrings = {};
     try {
-        localizedStrings = await fetchJson(localizedStringsUrl);
+        const res = await fetch(url);
+        if (!res.ok) throw new Error(res.status);
+        return await res.json();
     } catch {
-        if (localizedStringsUrl !== fallbackUrl) {
-            localizedStrings = await fetchJson(fallbackUrl).catch(() => ({}));
+        if (url !== fallbackUrl) {
+            try {
+                const res = await fetch(fallbackUrl);
+                return await res.json();
+            } catch {
+                return {};
+            }
         }
+        return {};
     }
-
-    return localizedStrings;
 }
 
 const languageNames = import.meta.glob('./*.json', {
@@ -38,5 +34,45 @@ function getLanguageName(code) {
     return String(languageNames[`./${code}.json`] ?? code);
 }
 
+/**
+ * @param {string} systemLanguage - BCP-47 code from AppApi.CurrentLanguage()
+ * @param {string[]} codes - supported language codes
+ * @returns {string | null} matched language code, or null
+ */
+function resolveSystemLanguage(systemLanguage, codes) {
+    if (!systemLanguage) return null;
+
+    // Exact match (e.g. zh-CN → zh-CN)
+    if (codes.includes(systemLanguage)) {
+        return systemLanguage;
+    }
+
+    const lang = systemLanguage.split('-')[0];
+
+    // Chinese: script-tag and region-aware mapping
+    // BCP-47 forms: zh-CN, zh-TW, zh-Hant, zh-Hans, zh-Hant-HK, zh-Hans-CN, etc.
+    if (lang === 'zh') {
+        const parts = systemLanguage.split('-').slice(1); // everything after 'zh'
+        const hasHant = parts.includes('Hant');
+        const hasHans = parts.includes('Hans');
+        const traditionalRegions = ['TW', 'HK', 'MO'];
+        const hasTraditionalRegion = parts.some((p) =>
+            traditionalRegions.includes(p)
+        );
+
+        if (hasHant || hasTraditionalRegion) {
+            return codes.includes('zh-TW') ? 'zh-TW' : null;
+        }
+        if (hasHans) {
+            return codes.includes('zh-CN') ? 'zh-CN' : null;
+        }
+        // Bare 'zh' or unknown region (e.g. zh-SG) → simplified
+        return codes.includes('zh-CN') ? 'zh-CN' : null;
+    }
+
+    // Generic prefix match (e.g. ja-JP → ja)
+    return codes.find((code) => code.split('-')[0] === lang) ?? null;
+}
+
 export * from './locales';
-export { getLanguageName, getLocalizedStrings };
+export { getLanguageName, getLocalizedStrings, resolveSystemLanguage };