Is it improper for people to speak a foreign language around others who cannot understand?

Answer 1

If there is a single language that everyone in your company can speak and understand, then you should probably use that language. If, for example, you are with a group of people in the United States and most of them speak English, but there are some that only understand Spanish, then you can definitely speak in Spanish to address those that don't understand English. Generally, it is not your responsibility to interpret everything you say in Spanish for the benefit of English-only speakers. If a speaker of English only asks you what you said, then you are obligated to either interpret what you said (e.g., "I asked whether that was true") or politely explain why you will not (e.g., "I'm sorry, it's private"). Courtesy does not require you to take on the role of running interpreter for the group, nor to repeat everything you say in more than one language, unless you need to address everyone in the group. You can, of course, do so if you wish, but you can also reject that role if you find it burdensome.