[Dr_ReD]

I would talk to the manager, explain what's happening, leaving my personal feelings aside.

Co-workers speaking non-shared languages in each other faces is not useful in any way and it leads to many problems, way beyond a non-welcoming and non-inclusive environment, way beyond just HR...

Moreover, and to answer some strange theories in other comments here, If you're to be excluded from a conversation, the speakers better get a room, where they can speak freely and leave you alone. Just staying around and speaking a language you don't understand is plain rude, a nuisance, and will distract you anyway. (and probably become annoying, in the long term)

Having said that, I would also learn some Mandarin. If not enough to enter the conversation, at least enough to say "Would you, please, be so kind as to speak English for me? I'm learning Mandarin, but I can't understand you well enough, yet."

This worked wonders for me, in more than a few occasions.

[dnqthao]

If they speak another language in the office but not with you (you are not part of their conversation), why is it rude? It is like a different channel where you will be less distracted by eavesdropping people.

[Dr_ReD]

Because it's disrespectful (non-inclusive and non-welcoming) to willingly bar someone who can obviously hear you, from understanding the conversation.

If you are "out of range", or in another room, then by all means, go nuts. Speak Elvish or even Klingon if that's your fancy. It won't bother anybody.

But in the presence of others, respect demands to let everyone understand. Even if the conversation is completely irrelevant to them.

And if you don't even apply basic respect, when others will start assuming the worst about your conversations, than that'll be your fault. You'd have brought it on yourself. Not "them", not HR—which sooner or later is going to be brought into the conversation...