About half of the team are from Finland and half from India. As the mother tongue of the team members varies the teams common language is english and it works out just fine most of the time. The language barrier does bring it's own challenges, here's a few that I have noticed or been informed of.
Challenge with conversations
Mostly out team struggles when it comes to ad-hoc conversations on implementation details or architectural decisions when we, the finnish team members, start to talk about it, in finnish, and thus leaving half of the team out of opportunity to join the conversation just because were talking in finnish and they have no idea what we're talking about.
This could be resolved by speaking only english when the topic is work related but to me that feels unnatural. Because it feels unnatural to speak english to another finnish speaking person it's probably why it's also so hard to remember that we should be speaking english.
Challenge of understanding
Another thing that happens occasionally is misunderstanding. Everybody is speaking english that no one speaks for a mother tongue sometimes leads to situation where a message might get misunderstood at the start or along the way as it passes from person to person.
It's not a huge problem as we tend to keep our individual tasks small but it does create some extra work in a form of refactoring or rewriting code. This does happen also when people have the same mother tongue but not as often.
Overall I don't see big problems working in a multilingual team but this is my first time as it probably is for some of the other team members also but it does bring some challenges. Hopefully we'll get better at it over time.
At least the next time I join a multilingual team I'll have a better idea what to expect and hopefully some solutions on how to over come or reduce the challenges.