In this site, what questions are considered to be on-topic and what questions are instead off-topic?
On Topic questions
Questions about any natural language from a linguistics point of view.
Linguistics phenomena during history.
Questions about the Linguistics subcategories.
Questions about currents, theories, and their applications in actual languages.
Questions about a single word in relation to multiple languages.
Questions about papers/articles on a given topic. These are ok, but make sure the question is as scoped and as specific as possible in order to avoid ambiguity.
Questions about a single word/single language. We decided to set such questions on topic, because they can bring up interesting facts, but with certain conditions. (1) The user provides evident research effort in their questions. This way we'd help you regardless of the difficulty of the question. :) (2) The question is more focused on the Linguistics aspect rather than the Usage one, because in that case it'd get off topic.
Anyway, these are guidelines to help everyone provide a better service. If you aren't sure whether your question is on topic or not, you can ask us before you post it, either on Meta or in Chat. Don't worry if there is no-one in chat at that moment, you can leave the message there and we'll reply as soon as we see it. :)
Questions about Sign Languages and writing systems.
Questions about fictional/constructed/planned languages. After the Conlang SE was closed and subsequently deleted, we have decided to accept Conlangs. Please make sure to visit that link in order to see what kind of questions are OK for Conlangs, we might not be able to answer all of them. Esperanto had already been deemed on topic prior to that.
Off Topic questions
Apart from the questions considered off topic to any site (see the "What questions should I not ask here" section below), the questions described below are considered off topic:
Questions that are not about Linguistics and their subcategories.
Translation-request questions. Asking translations of any kind is off topic on this site. Language-related SE sites usually put this matter off topic if it's a simple question like "Translate this for me", i.e. providing context and personal efforts can turn that question acceptable. But this site is not meant for any particular language and Linguistics doesn't treat about translation.
Still, if your question is about the linguistics reasons for some translations in different languages, etc., then it can be accepted. It will be necessary to check each question, since it's not reasonably possible to treat each case here.
As you might have noticed, the form counts a lot. Many times the wording/phrasing of your question would make it on topic even if theoretically that question asked in a more simple manner would be considered off topic.