Saying learn English isn't constructive criticism, if anything its far from it.
Constructive criticism is anything that will help the author improve their game. Learning English will improve their game immensely, as the game is written in English. It is highly constructive.
The author not feeling like doing the thing you suggest doesn't make it not constructive. Especially since I would obviously have no way of knowing if they feel like doing it or not before suggesting it.