fix(i18n): prioritize user settings over Accept-Language header

The i18n middleware runs before UserAuth, so user settings weren't
available when language was detected. Now GetLangFromContext checks
user settings first (set by UserAuth) before falling back to the
language set by middleware or Accept-Language header.

model/user_cache.go

@@ -221,3 +221,13 @@ func updateUserSettingCache(userId int, setting string) error {
 	}
 	return common.RedisHSetField(getUserCacheKey(userId), "Setting", setting)
 }
+
+// GetUserLanguage returns the user's language preference from cache
+// Uses the existing GetUserCache mechanism for efficiency
+func GetUserLanguage(userId int) string {
+	userCache, err := GetUserCache(userId)
+	if err != nil {
+		return ""
+	}
+	return userCache.GetSetting().Language
+}