import { Admin } from "react-admin";
import vietnamesMessages from "@completejavascript/ra-language-vietnamese";
import polyglotI18nProvider from "ra-i18n-polyglot";

const messages = {
  vi: vietnamesMessages,
};
const i18nProvider = polyglotI18nProvider((locale) => messages[locale]);

<Admin locale="vi" i18nProvider={i18nProvider}>
  ...
</Admin>;