I am a course contributor for a four-part Swedish-English course (8,000 Most Common Swedish Words) and there are many many people who use this course whose first language isn’t English. There are mems in Arabic, in Hebrew, Chinese and an Eritrean language on this course. I haven’t flagged or deleted ANY of them.
What’s more, there are also many people who emigrate to Sweden whose first language isn’t English, but might have a relatively good knowledge of English. This course being available in English might be very helpful to non-native speakers of English whose native language is not a very common one. And they might really welcome mems being available in their native language!
Seeing as Swedish is not a super-popular language, I think it is not my job to eliminate mems just because I personally don’t understand them. They might be understood by other people and be very helpful to them.
Mems are a personal subjective thing: what works for one person might not work for me, but that doesn’t mean it is not super-helpful to someone else.
Why not be happy that someone who speaks Chinese is trying to learn Arabic? It’s not their fault if your course happens to be the one that looks best to them.
Some people use learning a new language via a second language as a particular strategy to boost and solidify their knowledge of both the new language and their stronger second language.
I think there is nothing wrong whatsoever in allowing Chinese mems on an Arabic course. English is an international language and native speakers of English don’t “own” it.