It's not a dumb question. The answer is "it depends", it's mostly a choice. The general rule is that when yo start a project, you choose the language that you think will help you the most, whether that is because you already know the language, or because you have to work with stuff that already use that language, or because the language is better at doing that.

Regarding whether to stick to a language or learn a new one, in general your CS teachers will tell you (and they are correct) that you should not "learn to program in a language" but just "learn to program" and then apply that knowledge to whatever language you need. So, you should always learn languages that are different from the ones you already know in order to learn new paradigms, and then when you need a specific language, just learn the details about it. BUT, even if this way you will be able to use most languages, you will not be "good" at most, so you should also have some languages that you know really well and are experienced in. And for that you should choose the ones that are more useful to you (or maybe useful for your job) or the ones that you like.