Filter menu parent dropdown by language for multilingual site?
This seems to be the issue page for this problem: https://www.drupal.org/node/1242288. There are patches but as Jose Reyero points out, it would be only a partial solution.

There is a https://www.drupal.org/project/content_menu which enables you to first deal with the menu and then with the content instead of vice versa. Haven't tried but seems nice. This combined with Fixed language menus (provided by Menu Translation at admin/structure/menu/manage/menu-mymenu/edit, Multilingual options - Translation mode) could clean up the menu interface nicely.

Personally, I usually just don't bother dealing with the Parent item, I just head to the menu interface after creating a node, and drag my item, which will be at the bottom, to its place.