> I can't tell what they [commits] contain until I open them one by one [because they are not in english]
I'd hope the diff does this for you, and I'd also hope you don't go solely on commit messages to see what they contain! If you're reviewing PRs you don't have to check each commit anyway. And I hope it's not true that if you're reading the commit msgs (instead of top-level change) and getting mad when they don't make sense.
It might be I misunderstand your question. At any rate, yes, ask for translation if you need it to be satisfied with the PR.