If I wanted to write fiction about a place I've never been before (which I, in fact, do), how could I possibly learn the fundamentals of the language enough for names of fictional places within that setting?

I’m a little confused. Are we talking about a place that is not English speaking?

I think you take some risk writing about a place you have never been, but I do think you can probably get quite a bit of help online. If you are writing a book you don’t need to worry about pronunciation, just spelling and usage. Like knowing people say The Bronx, not just Bronx, and that people who suburb NYC simply say, I went into the city, when talking about Manhattan.

If you are writing in English for an American audience you only really need to know common usage in English. I think an editor can help you once you have the work done.

Maybe I don’t fully understand the question though.

Are you writing fiction set in a real place or an imaginery place?

Fictional places? You can name them anything.

My current comic is about a fictional city in France, and I also have knowledge of French. And I have to disagree that language courses only provide you with conversational knowledge. If you learn to absorb the language actively and have a keen eyes on details, you will learn a lot about the culture and etymology. That, and a little bit of good research, is why I’m able to write my comic to some degree eve though I have never been in France.

But yeah, if you are to learn a language only to write a book that’s going to be a bit of a stretch. You can go online and ask people with your etymology questions.

JRR Tolkien wrote fictional people, events, and places etc
Make up your own world and call it anything.
Use a scrabble game to make up names..lol

Read Watership Down:

https://en.wikipedia.org/wiki/Watership_Down