Is it bad manners to speak a foreign language in public?

No, as long as everyone in the group speaks the language there is nothing rude about speaking it. People who have an issue with other people speaking something other than English have an issue. Either they think they have a right to eavesdrop, or they are just plain racist. Likely both but it’s mostly racism. It’s interesting because I’m Caucasian and my spouse is Asian. We will sometimes speak in his native language. Which isn’t even the main language in the country he was born in but a dialect. Outside of a few specific locations in the US where there are decent sized populations who speak it (we met and used to live in one) you won’t come across too many people around the country who even can recognize what the language is much less speak it. We’ve never had an issue when we speak it in public with each other and I’m sure that is partially because I’m white. The racists don’t know how to process this white person speaking a clearly non European language with a non white person. It’s also interesting that many of my in laws speak French as well. Some are also Asian and some are white and we’ve never had any issues speaking French in public. But I have friends who have had comments made when not speaking English in public and when all the people in the group are not white. So to me it’s really just racism. And so fuck the racists. In the US you have every right to speak any language you want with others, and it’s no one’s business. And anyone who makes it their business is the one being rude.