@HR and ME,
Well -- and I'm going to throw out the languages but they're probably wrong. This is just to make it easy for me to explain.
Let's say you're Chinese, and the HR people are Japanese. You agree to have lunch, or, perhaps, they see you and say, come and join us for lunch. You come and you eat with them but they've got some Japanese pals with them, and they spend a good 90% of the time speaking Japanese to their pals -- a language that you don't understand.
Now, I could get it if it was a word or two. Or, perhaps, if it was that they were going along in English and there was some word they didn't know and they threw it out in Japanese (several years ago, I used to work with 2 women who were Mandarin speakers -- they would be speaking Mandarin to one another and then English words like database
would be thrown into the mix as well). None of that would be a problem.
The problem is that most of the conversation is automatically excluding you. It's probably not about you (and it's worse if it is, but let's assume they're not gossiping about you while you're sitting there). The act is just plain rude.
But you can interject -- I don't understand you -- could you repeat that in English -- is that about someone I know. And also drive the conversation a bit yourself, e. g. bring up the topics. And don't be afraid to be very direct and say to the HR folk -- when you speak Japanese, I can't understand you and I feel very excluded when you do that.
They may truly not get that it's rude (yeah, I know, it should be obvious, but some people are really that out of it).
I would say, try this, maybe, three times. If the problem persists, though, I'd say these people are clueless and rude and you might want to find other friends.