There's a lot of debate going on about questions and tags for individual languages. Personally, I think they should be on topic, as most people on here will be learning (or teaching) one or more specific languages.
However, one idea might be to lean more towards language groups, such as Romance Languages, Slavic Languages, etc, on the basis that the process of learning one language in a group would be similar to another?
Some questions apply to language families, but I doubt that it's the majority. Language families are mostly grouped by vocabulary, they can have rather different grammar, spelling, phonology, etc.
A tag like romance-languages on a question about, say, how to train oneself to pronounce the letter R, or when in a curriculum to teach the subjunctive, would be meaningless. Such a question should be tagged french or spanish or italian etc. as appropriate: these questions have completely different answers in different Romance languages.
There are questions that apply to a set of languages, not necessarily grouped by historical families. Such questions should be tagged according to what makes the question distinctive. For example, a question asking specifically about leveraging similarities between Romance languages should be tagged romance-languages. A question asking about teaching language features such as tones, cases, etc. should have a tag corresponding to that language feature.
Some questions apply naturally just to some language groups. For example, my question What are the pros and cons of learning noun classifiers along with vocabulary? is only useful for languages with classifiers.
However, I don't think that creating tags or questions for language groups is such a good idea.
