diff --git a/src/i18n/index.ts b/src/i18n/index.ts
index 1fab0ca4..fba29835 100644
--- a/src/i18n/index.ts
+++ b/src/i18n/index.ts
@@ -33,7 +33,9 @@ export const i18nResources = [
     'vi',
     'zh_Hans',
     'zh_Hant',
-];
+] as const;
+
+export type I18nResourceCode = (typeof i18nResources)[number];
 
 export const i18n = use(initReactI18next)
     .use(HttpBackend)
diff --git a/src/util/isoLanguages.ts b/src/util/isoLanguages.ts
index 1859f558..31276278 100644
--- a/src/util/isoLanguages.ts
+++ b/src/util/isoLanguages.ts
@@ -6,9 +6,9 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/.
  */
 
-export const loadDefaultDayJsLocale = () => import('dayjs/locale/en.js');
+import { I18nResourceCode } from '@/i18n';
 
-export type ISOLanguageCode = string;
+export const loadDefaultDayJsLocale = () => import('dayjs/locale/en.js');
 
 export type ISOLanguage = {
     name: string;
@@ -17,7 +17,7 @@ export type ISOLanguage = {
 };
 
 // full list: https://github.com/meikidd/iso-639-1/blob/master/src/data.js
-export const ISOLanguages: Record<ISOLanguageCode, ISOLanguage> = {
+export const ISOLanguages: { [languageCode in I18nResourceCode]: ISOLanguage } & Record<string, ISOLanguage> = {
     // #############################
     // ###                       ###
     // ### START: manually added ###