fix: sync language prefixes

src/i18n.tsx

@@ -5,7 +5,11 @@ import React, {
   useMemo,
   useState,
 } from "react";
-import { languageForHomePathname } from "./languageRoutes";
+import {
+  languageForHomePathname,
+  languageFromPathname,
+  langPathPrefix,
+} from "./languageRoutes";
 import type { Dict } from "./locales/types";
 import { zhDict } from "./locales/zh-CN";
 import { enDict } from "./locales/en";
@@ -40,9 +44,14 @@ const LANG_KEY = "ark_lang";
 
 export function I18nProvider({ children }: { children: React.ReactNode }) {
   const [lang, setLangState] = useState<Lang>(() => {
-    const routeLang = languageForHomePathname(window.location.pathname);
-    if (routeLang) return routeLang;
-    if (window.location.pathname === "/") return "en";
+    const path = window.location.pathname;
+    // Any URL whose first path segment is a known language prefix wins
+    // (covers /malay, /malay/browse, /korean/category/foo, etc.).
+    const homeLang = languageForHomePathname(path);
+    if (homeLang) return homeLang;
+    const deepLang = languageFromPathname(path);
+    if (langPathPrefix(deepLang)) return deepLang;
+    if (path === "/") return "en";
 
     const s = localStorage.getItem(LANG_KEY);
     if (s === "zh" || s === "zh-TW") return "zh-CN";

src/layouts/PublicLayout.tsx

@@ -15,6 +15,7 @@ import {
   homePathForLang,
   isHomePathname,
   languageFromPathname,
+  localizePath,
   stripLangPrefix,
 } from "../languageRoutes";
 import { useLocalizedPath } from "../useLocalizedPath";
@@ -318,7 +319,15 @@ export function PublicLayout() {
   const homePath = homePathForLang(lang);
   const changeLang = (nextLang: Lang) => {
     setLang(nextLang);
-    if (isHome) nav(homePathForLang(nextLang), { replace: true });
+    if (isHome) {
+      nav(homePathForLang(nextLang), { replace: true });
+    } else {
+      // Preserve sub-path and query/hash; only swap the language prefix.
+      const canonical = stripLangPrefix(pathname);
+      nav(localizePath(canonical, nextLang) + search + hash, {
+        replace: true,
+      });
+    }
   };
   const footerInContentFlow = stripLangPrefix(pathname) === "/browse";
   // Current page name shown in the header brand slot (falls back to the brand).