feat: align frontend languages with posts api

src/components/messageStream/hooks/useGroupedByDay.ts

@@ -8,9 +8,16 @@ export type DayGroup = {
 };
 
 function localeFor(lang: string): string {
-  if (lang === "zh-TW") return "zh-TW";
-  if (lang === "zh-CN") return "zh-CN";
-  return "en-US";
+  const locales: Record<string, string> = {
+    zh: "zh-CN",
+    en: "en-US",
+    ja: "ja-JP",
+    ko: "ko-KR",
+    vi: "vi-VN",
+    id: "id-ID",
+    ms: "ms-MY",
+  };
+  return locales[lang] ?? "en-US";
 }
 
 function dayKey(iso: string): string {
@@ -28,12 +35,10 @@ function dayLabel(iso: string, lang: string): string {
     a.getMonth() === b.getMonth() &&
     a.getDate() === b.getDate();
   if (isSameDay(d, today)) {
-    if (lang === "en") return "Today";
-    return "今天";
+    return lang === "zh" ? "今天" : "Today";
   }
   if (isSameDay(d, yesterday)) {
-    if (lang === "en") return "Yesterday";
-    return "昨天";
+    return lang === "zh" ? "昨天" : "Yesterday";
   }
   return new Intl.DateTimeFormat(localeFor(lang), {
     month: "long",