Is speaking a foreign language at work rude?
It can be rude, but it depends on the situation. I live and work in Japan, and my native language is English. Everyone in Japan studies English in middle and high school, so theoretically they should understand English. In practice, only a handful of people understand even simple sentences spoken slowly, much less full-speed slangy English.
I speak Japanese most of the time I’m at work, unless someone wants to use English when speaking to me. I don’t work with any other English speakers, but if I did we would probably use Japanese most of the time. I can easily see chit-chat and other minutia defaulting to English if I did have an English-speaking co-worker. Anything work related, or that included someone else in the office would go back to Japanese.
I’d never talk shit right in front of someone in English, even if I thought they wouldn’t understand. You’ve either got to be a total self-centered douchebag to do something like that, or have big swinging brass balls and not give a flying fuck what someone thinks about you. Even if you don’t get “caught,” it shows callous mean spirit toward everyone else around you.
At informal occasions the way it usually works out is: if we’re with the main group, everyone uses primarily or exclusively Japanese; if we split off into a majority English-speaker group, we use English with asides in Japanese for the benefit of the one or two people who aren’t fully fluent and decide to stick with that group.
I’ve also had a few occasions where we were all using a non-primary language to communicate, like with my wife’s Flamenco group — which obviously has some native Spanish speakers — or with a group of Chinese. Usually, we’ll use Japanese even among a group that doesn’t include Japanese people since it may be the best common language (I understand Spanish pretty well, but it’s been 15–20 years since I spoke it, so everything comes out garbled Japspanglish if I try to reply). I have had situations where the native Chinese speakers wanted to use English with me even though our mutual Japanese level was possibly higher than their English level. I figure they either wanted to practice, or thought I might be more comfortable in English and they didn’t mind.
Really, language choice depends on the group dynamics. Most people try to accommodate the intended audience. If people are choosing a language you don’t understand in order to exclude you, it’s because they’re shitty people who would exclude you even if they were speaking your language. Forcing them to “include” you by making them speak your language isn’t going to change their personalities.
If they were talking about you or insulting you in their language, the only difference might be that they have to confine their backbiting to times when they aren’t right there with you, just like the rest of your co-workers. What? You do know that ALL your co-workers insult you behind your back, not just the Filipinas, right?