whaticket-community/frontend/src/App.js

import React, { useState, useEffect } from "react";
import Routes from "./routes";
import "react-toastify/dist/ReactToastify.css";

import { createMuiTheme, ThemeProvider } from "@material-ui/core/styles";
import { ptBR } from "@material-ui/core/locale";

const App = () => {
	const [locale, setLocale] = useState();

	const theme = createMuiTheme(
		{
			palette: {
				primary: { main: "#1976d2" },
			},
		},
		locale
	);

	useEffect(() => {
		const i18nlocale = localStorage.getItem("i18nextLng");
		const browserLocale =
			i18nlocale.substring(0, 2) + i18nlocale.substring(3, 5);

		if (browserLocale === "ptBR") {
			setLocale(ptBR);
		}
	}, []);

	return (
		<ThemeProvider theme={theme}>
			<Routes />
		</ThemeProvider>
	);
};

export default App;