There's a lot of different factors. I already have a wide range of interests, so sometimes it's something I happened to like already, but sometimes a friend or acquaintance will show me something that they think is interesting and I'll look more into it. The latter is how I found out about that Den Faminico Gamer interview about The Caligula Effect, among other things.

As for what makes me decide to translate something, I usually take a number of things into account, such as how much it personally interests me, how much "urgency" it has (i.e. if it hasn't been translated yet, or its existing translation is bad to misleading levels), how much time it'll take me to do, and whether it'll be a fun challenge for my translation skills. I've translated things that I'd never heard about before a friend pitched it to me, but I've also translated things that I just happened to personally like so much that I'd do it even if someone else translated it already. Of course, it definitely helps if I happen to like the contents itself; I can still enjoy the experience of translating something and put a proper effort into it even if I'm not fond of the actual contents (a lot of the interviews I've tackled come to mind), but I only have a limited amount of free time, so I'm more motivated to spend time on it if I'm a fan...😅