Personally, assuming its the local language, I’m fine with the idea.

People who are multilingual don’t always seem to get how it looks/feels for monolingual people – but it’s a way of excluding them from participating in whatever the conversation is. I think back to a camping trip described by an X with her friends, where in most of the group spoke english and chinese – except my X, who only spoke english. Because one or two in the group were more fluent in Chinese, for most of the weekend the vast majority of conversation was in Chinese, which really drove home how isolating / alienating it can be to be the person left out. You’re basically being pre-excluded from a conversation, just to make it easier for communication with someone else – your basic participation is less important than the other person’s ease of communication. My X had no concern about them “talkin bout her behind her back” or anything, they were all friends, but she finally understood how it comes across.

While the majority of the work force may speak another language, the “main” language in a country is to me, meant to serve as a default for business. If I were multilingual, working in a foreign non-english country, I’d expect any business I worked for to require me to use their local language. Even more, when it comes to supervisors/team leads, hearing the conversations can also help you target potential issues – like if you overhear a team member teaching something incorrectly. So there’s a potential business liability type reason to make sure that all team members, especially oversight, can understand what’s getting said if it pertains to the business.