Just keep your locale set to japanese unless you absolutely need to change it. It doesn't really affect anything on your computer and it certainly won't make everything Japanese. The only thing in my experience that will change is some setups will change to japanese on installers that do have the Japanese language bundled in there. Even those programs end up installing in English for me.
Edit: Most VN's only play in Japanese locale since they are written in Japanese unicode ( Please correct me if I'm using the wrong terms.)
What VN are you talking here? If you can't read it, it probably means it isn't fully translated.
Here is an example of an incomplete project:
Here is an example of a complete project:
It's cool, I'm used to being communities where donating is a normal thing (MPGH, BakaBT, ETC.) to keep things running ultra great, and when I joined here everything seemed so nice that I thought I might have missed the donation box.
I feel the hardest part of the transition between the anime they love so much to actually playing the visual novel is the acquisition of the VN. Most people are too lazy to download anything even though it's quite a simple process. Maybe someone should make a video on to do everything in like 5 minutes, to get them over the fence because I know visual novels are definitely worth the effort!
NouKome and WA2 are the two I've been actively keeping up with. I watch Log Horizon every 2 weeks since it'll keep me until the next showings of the anime. Nagi no Asukara is definitely a show I didn't expect to be interesting but so far its pretty good.