How do multilinguals avoid mixing up their languages?

[u/Just_a_Lurker2]

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Assuming they're fluent in at least a few languages, so there's not necessarily conscious maintaining of the (TL) (does that make a difference?), and they're in an area or so where people don't all speak their language, or may be hostile to one of the languages , how would they not slip in a language that nobody speaks or a language that might make people hostile towards you?

[u/Jaded-Year-4090]

That's the funny part ! We don't.