If you are, then personally I think it is really bad form for the other team members to be speaking in a foreign language when the native English speaker is present.
It's rude and disrespectful and I think it's bizarre that we are in this contemporary situation where we are afraid to say that.
If I was working in a foreign country where the native language was - as you would imagine - that spoken in the office, I would damn well learn it and feel embarrassed at co-English speakers excluding somebody on the team who couldn't speak English.
I can't offer a "tactful" answer beyond having an informal chat with somebody you trust with influence, and even that might be risky in the wrong environment.