I frequently converse in three languages: Hindi, English and Marathi - all with distinct sets of acquaintances. Likewise, every person has a preferred communication language with every other human they are acquainted to.
Occasionally, two of my acquaintances meet and have a different preferred language. If I’m not acquainted to that language, all’s usual. But if I am acquainted to that language and they are aware of that: they might request me to converse in that language.
This usually happens for all three possible pairs of Hindi, Marathi and English.
What happens next is fairly awkward: I’m stuck between two modes of communication and stutter for a good half minute with a jaw-dropped (my first aware use of a passive adjective) smile of embarrassment.
Hence, have been explicitly forcing myself to converse in different languages with the same acquaintance and switch fairly smoothly, for a few days.
Now I switch easily.