You might also want to add the adapterLocale to your LocalizationProvider

import { AdapterDayjs } from '@mui/x-date-pickers/AdapterDayjs';
import 'dayjs/locale/de';

<LocalizationProvider dateAdapter={AdapterDayjs} adapterLocale="en">
  {children}
</LocalizationProvider>;

Reference: https://mui.com/x/react-date-pickers/adapters-locale/