Rename en to en-US.

lib/lang.js

@@ -1,6 +1,6 @@
 import { format } from 'date-fns';
 import { enUS, nl, zhCN, tr, ru, de, ja } from 'date-fns/locale';
-import enMessages from 'lang-compiled/en.json';
+import enMessages from 'lang-compiled/en-US.json';
 import nlMessages from 'lang-compiled/nl-NL.json';
 import zhCNMessages from 'lang-compiled/zh-CN.json';
 import trTRMessages from 'lang-compiled/tr-TR.json';

redux/actions/app.js

@@ -2,7 +2,7 @@ import { createSlice } from '@reduxjs/toolkit';
 
 const app = createSlice({
   name: 'app',
-  initialState: { locale: 'en' },
+  initialState: { locale: 'en-US' },
   reducers: {
     updateApp(state, action) {
       state = action.payload;