How to change the font family in TinyMCE

How to change the font-family in an external editor if the following construct doesn’t work:

add_editor_style('css/editor-style.css')

in functions.php, and next:

function new_font_for_tinymce( $mceInit ) {
  $font_family = get_theme_mod( 'font_family' );
  $styles = '.mce-content-body { font-family: Roboto' . $font_family . '; }';

  if ( !isset( $mceInit['content_style'] ) ) {
    $mceInit['content_style'] = $styles . ' ';
  } else {
    $mceInit['content_style'] .= ' ' . $styles . ' ';
  }
  return $mceInit;

}
add_filter( 'tiny_mce_before_init', 'new_font_for_tinymce' );