What do we lose when we learn a new language? Flip sides of the same coin:
- The ability to completely ignore those around us speaking in that language.
- Resistance against misinterpreting random sounds as speech.
On the 2nd point, an expanding phonetic library necessarily diminishes the open space into which it expands, such that, within the set of all sounds, the size of the subset of sounds to which the mind hasn’t yet associated a language is reduced. It’s worth noting that the set of all sounds refers to nothing less than the whole of the variety of acoustic vibrations perceptible to the human ear. While it’s more likely that a random sound is misinterpreted as speech if it’s a verbal utterance than if it’s e.g. a wind’s whisper, the wealth of sounds whose origin is not a human mouth have, collectively, a nonzero susceptibility to being misinterpreted as speech.
One wonders how much neural network overlap there is between areas of the brain involved with understanding one language vs another. Suppose, for example, that you were equally fluent in two languages, A & B, but, in anticipation of being in the midst of people speaking in B while endeavoring to engage in private introspection, wished to temporarily unlearn B for the sake of not losing ability #1 above. Intuitively, the lesser the neural network overlap between languages, the better able one would be to selectively disable their understanding of a given language. That there are different neural networks involved in knowing different languages is supported by accounts of multilingual stroke survivors being able to communicate in a subset of languages previously known.
Perhaps neural implants will one day facilitate temporarily disabling knowledge of a given language. Until then, are the losses associated with learning a new language offset by what we gain? Absolument!