does it make sense to have questions only in Arabic
Yes, but it could also make sense to try and promote two editions, one being English, where possible for questions that can be easily worded into English; displaying the two side by side, like: ماذا سنفعل بالمشاركات التي تنسخ العربية بحروف أجنبية؟ What to do about transliterated posts
This way, beginners won't be excluded from some knowledge that might be very interesting.
I totally agree, I am not an advanced speaker of Arabic, however, I am competent with the language enough to read with the aid of looking up word roots and the meaning of new words (I am not a native and have never even met an Arab in real life so I cannot know every verb in the language) in a dictionary.
I would feel left out if some really good information was solely in Arabic, however, you must understand that some questions and answers can only be expressed in Arabic as such there will always be questions and answers which will not be easily decipherable to learners/non-native speakers without considerable translation time spent; this is, afterall, a proposal for all Arabic speakers, including Academics.
Many Arabic speakers will be quite loathed to actually have to ask their question/answer questions in English, to reference an answer I got recently from another contributor of this proposal: https://area51.meta.stackexchange.com/a/17303/112766
I am personally 70% against english questions about Arabic.
So you canot expect people to give courtesy to learners on this proposal but I do agree that some needs to be given for general topics which could be helpful and insightful to all.
Afterall is not this site about sharing?
Since English is an extremely common language that binds to so many millions/billions of internet users it is hard to say that questions on here should not be given the chance to have an English edition, side by side with Arabic (personally I would prefer that actually than plain English) in order to spread the wealth that Arabic has to offer to alll; a.k.a sharing.
So to sum up: I would really like the wealth of Arabic to be spread to a greater audience making this proposal appeal to many more people by adopting English for some questions but you cannot expect it, nor demand it.