The primary question is, what should constitute "off topic"?. We also have to figure out how to communicate that viewpoint in the help center. The four specifically off-topic areas are:
Advice or help on learning a foreign language
"Please make me a syntax tree" — Don't ask us to solve your homework
problems for you, but it's OK to ask questions that would require
drawing of syntax trees to gain a better understanding of the subject,
so that you can learn to solve the homework problem on your own
Identification of a language or a script based on specific samples
and/or its translation — Questions about the scholarly aspects of
translation and language identification are still welcome.
2 is a subcase of 4: 2 can be deleted. I would rewrite 4 as "Translation or identification of samples of a language or a script. Questions about the theory of
translation and language identification are still welcome". 3 misses the boat. It's not about trees, it's about "do my homework", "solve my problem" questions. Put simply, "Don't ask us to solve your homework problems or answer your test questions for you". Even if the most common offender is syntax trees, that does not justify making it seem that (a) questions about syntactic trees i.e. constituency are OT and (b) asking for answers to phonology problems is on-topic. At the moment, I have little to say about the language-learning ban.
Questions about proper grammar, proper usage – the normative questions – already have an SE-wide close reason: "primarily opinion based". It seems to me that we do not need to do or say anything special, although seasoned users may need to get on board with the idea that primarily opinion-based questions should be closed (this reason is under-utilized). What remains of the "language specific" reason is that it refers to non-generalizable questions.
My proposal is that we need to dump the "language specific" way of thinking about the matter, and instead focus on the problem of non-generalizability. Saying "Don't ask non-generalizable questions" is too vague, but still, I propose this as a target statement. Is there a general class of non-generalizable questions that we would like to encourage or at least tolerate?