Do snack bars in any Japanese town/city allow foreigners? I mean, I get it, these aren’t places foreigners should be going, but their forbidden nature always raises eyebrows.
Snack bars aren't anything forbidden or erotic, they're bars where women are employed to speak to the customers and entertain them (again, not in an erotic way), that's it. I live in a suburb with lots of them around, it's not some kind of red light district filled with brothels, they're just bars I pass that usually have badly sung karaoke blasting out.
I also don't understand the replies you're getting as they seem to have run with this misconception, I can't be sure these people have even visited Japan!
Also, you're expected to be on your BEST behaviour. DO NOT EMBARRASS PEOPLE, because the responsible person will suffer for it (not you, but please, don't be a dick).
Actually, if you want to get a peek at what the underbelly looks like (with a lot of creative license of course), check out "The Naked Director". It was quite refreshing compared to the regular pablum of Japanese television.
I haven't been to many, so I can't really speak to that. I tried a few times and had no trouble getting in, but I was with Japanese friends. May have been a different story if I had been alone.
This is not to say there is no racism in Japan, but for resorts it's most likely they don't have the capacity to help in English/Foreign Language.
If it's some seedy thing, like a cheap/seedy bar, karaoke, J/KTV or sexual services then it's both, no English and they want discretion.