I think, therefore IB

Research into how multilingual people manage multiple languages in their minds is fascinating and sometimes surprising.

When a multilingual person speaks, all the languages they know can actually be active at once, even if only one language is being used. These languages can sometimes “intrude” unexpectedly, showing up not just in occasional vocabulary mix-ups, but even in subtle ways like grammar or accent shifts.

Read this interesting BBC article for more on the topic.