English isn’t my first language (I struggled to learn English as a kid) and I rather heavily disagree with this statement.
There’s nothing about the situation that’s acceptable. Communicating well is arguably the most important thing in any knowledge workers job and this is already a difficult task for some people even when they all speak the same language.
Obviously in this case it’s valuable for the team to be able to explain things for the non English speaking employee but that shouldn’t turn into a situation where Mandarin becomes the default. Additionally they are doing a massive disservice to the employee who isn’t yet comfortable with English.
It should be possible for OP to express such a view from a position of strength without coming across as an asshole (https://youtu.be/HbvYeLxMKN8) and without feeling self conscious about it as many monoglots seem to be in these sorts of situations.
I’ve worked closely with a multinational technology company based out of Germany that had a lot of Spanish, Italian, and French speakers and there was most definitely an obligation to speak English, even at the headquarters in Germany where the number of native English speakers could be counted in single digits.