Why can't we all remember 20 different languages, then?

It seems it takes a surprisingly small amount of memory storage to know how to use English:

A pair of researchers, one with the University of Rochester the other the University of California has found that combining all the data necessary to store and use the English language in the brain adds up to approximately 1.5 megabytes. In their paper published in the journal Royal Society Open Science, Francis Mollica and Steven Piantadosi describe applying information theory to add up the amount of data needed to store the various parts of the English language.

If only the brain was flash memory chips instead of stupid wet cells, then...