Margin problem on management menu?

You can’t modify WordPress’ admin CSS. Well, technically you could, but it’d just get overridden the next time you update WordPress.

The solution to this is to add your own custom CSS file to override the parts you wish to.

In your theme’s functions.php, you can add a new CSS file to be loaded only in the WordPress admin:

add_action("admin_enqueue_scripts", "my_enqueue_scripts_admin");

function my_enqueue_scripts_admin(){
  wp_register_style("my-admin-css", get_template_directory_uri() . "/admin.css", array(), "1.0", "all");
  wp_enqueue_style("my-admin-css");
}

Then, create a file called admin.css in your theme’s root directory. In here, you can add the CSS to directly target the relevant class or ID on the menu page.

In your case, it looks like #menu-management-liquid might be the ID you need to target. You could do #menu-management-liquid { margin-left: 100px; } to move it over a bit, or you could instead target the language list and limit it’s width or make it wrap (I’d probably prefer this option – otherwise you could be moving the entire menu management section a long way over!)