Hi. Please help.
I think the word "vocabulary" denotes, possibly among some others, all the words a person knows or a language contains (not sure, though). Anyway, then what does the plural "vocabularies" denote? Thank you in advance..
'Vocabularies', in its very restricted usage, is used when comparing all the words known by each of several different individuals, for instance, or the different sets of words used by different dialects, etc.

We use the word "vocabulary " if we are talking about a set of words in one language whilst we use "vocabularies" if we are talking about words in several languages.