Simple Admin Language Change

The lightweight plugin extends the default functionality and pulls out the language selection to the admin bar so you can easily switch between them.

Customization

Use the salc_languages filter to control which languages appear in the dropdown:

add_filter( 'salc_languages', function ( $languages ) {
    $allowed = array( 'en_US', 'cs_CZ', 'de_DE' );
    $languages['available'] = array_filter(
        $languages['available'],
        function ( $lang ) use ( $allowed ) {
            return in_array( $lang['value'], $allowed, true );
        }
    );
    return $languages;
} );