For me, I chose to study Japanese at university but I was always better at speaking it rather than reading it. My kanji (the Chinese characters used in Japanese text) is for complete shit so that makes reading things in games kind of difficult at times. It's only in the last few months that I've bothered to try and improve this and as a result it's been a little easier to play certain titles. For example, I'm not at a point where I could play games like Mind=Zero or Persona 4: Dancing all Night with not much trouble but certain games like Bloodborne are still tripping me up pretty hard.
|This is basically the games objective but I had no idea for ages because I just dismissed this horrible wall of kanji|
Another good reason to get your head round the language is that while a lot of games do get brought over to the west, there are a pretty good number of good ones that don't. I'm sure any fan of Japanese games has had that moment where they see something that looks really cool but then get sad because they hear it's not being translated. Well you won't have to worry about that shit anymore and with things like PS4 having no region locks you're free to play whatever the fuck you want.
Aside from all the gaming stuff, learning another language is just kind of useful in its own right. Sure, you could argue that there are more "useful" languages to learn but we're not trying to build a career here, we're trying to play some damn games. Hell, Japanese isn't exactly a dead-end language, learning it for the sake of gaming may be that first step into some kind of successful career, who the fuck knows?!
Either way, if you like video games, especially Japanese ones, getting your head around some Kanji and Grammar seems like a good idea. Whatever happens after that is just a bonus.