Are language questions such as "What language did the Hittites speak?" or "Why did Arabic replace Aramaic?" on topic?
Do they belong on the Linguistics beta site instead?
We are discussion lots of different nations, countries and tribes here, and there are obviously different aspects to consider, e.g. religion, tradition, origin and language. It would be illogical if we could ask "What was the religion of Visigoths?" but not "What language did Visigoths speak?". IMHO, most language questions should be on-topic:
I would only consider questions off-topic that only refer to the language itself and would indeed belong into the field of linguistics:
The general rule is that, if a question is on-topic on more than one site, it's up to the asker to decide where to post the question. Heck they can even post the question on different sites as long as they tailor the question to fit the specific site (i.e., not an exact duplicate).
The history of language, IMHO, should be on-topic.