use Intl.DateTimeFormat and Intl.NumberFormat instead of toLocaleString (#9444)

packages/frontend/src/scripts/intl-const.ts

@@ -0,0 +1,12 @@
+import { lang } from '@/config';
+
+export const versatileLang = (lang ?? 'ja-JP').replace('ja-KS', 'ja-JP');
+export const dateTimeFormat = new Intl.DateTimeFormat(versatileLang, {
+    year: 'numeric',
+    month: 'numeric',
+    day: 'numeric',
+    hour: 'numeric',
+    minute: 'numeric',
+    second: 'numeric',
+});
+export const numberFormat = new Intl.NumberFormat(versatileLang);