The Teams Windows and MacOS desktop clients will soon allow users to add a personal account to the set of Office 365 tenants they connect to. A great deal of excitement ensued after people saw Microsoft 365 roadmap item 68845 and assumed this meant that Teams would support connections with multiple work accounts. The ability to add more than one work account to your Teams profile isn’t available now as the update is to support connectivity to Teams at home (personal), but support for multiple work accounts is coming in the future.
The Windows desktop client for Teams monitors text as users type chat and channel messages to detect if they switch language. And if they do, Teams can change language for spell checking. The code runs on the client and no data is transmitted back to base. It’s all very intelligent, but you should warn users that it might happen.