Deutsch (Sie) Contact Form

by the way: you can have child-theme edited lang files –
just create in child-themes folder a lang folder
and put those edited lang files ( po and mo – in your case: de_DE_formal.po and de_DE_formal.mo ) to that folder.
Put this little snippet to your child-theme functions.php:

function overwrite_language_file_child_theme() {
    $lang = get_stylesheet_directory().'/lang';
    return $lang;
}
add_filter('ava_theme_textdomain_path', 'overwrite_language_file_child_theme');