I agree that it is very rude to speak in a foreign language in a group when even ONE person does not understand that language, regardless of the situation. The other members are obligated to divulge what transpired and when/if they don’t they are creating an uncomfortable situation for the non-speaker.
I don’t personally believe people are unaware they are being rude. Sometimes it is a subtle form of malice, control or domination. It’s the obligation of someone in that group to speak up and translate.
Blue, it sounds like you were trying not to rock the boat further by speaking up, but after the trillionth time it happened, it’s a moot point to even complain if you hadn’t made it a regular habit. It’s no fun pointing out other people’s social errors, but it’s worse being subjected to them on a continuous basis.
I suggest if this happens to anyone in the future (1) Let it slide the first time; (2) second time object (humorously or not, up to your emotions at the time); (3) Third time leave the room making your point being taken (ie zero tolerance). If you can’t leave the room, start a discussion why it is rude to talk in a language foreign to others, in a tone which suggests they don’t have the intellect to understand that without your merciful assistance.