Err.. I would suspect most(non-english?) people on the internet to know 2000 words. (By virtue of being atleast bi-lingual, they would, so the challenge boils down to can they type it? unicode support should help, but I've found most cases people simply type those sounds in English.) As for the English as a primary language people, I've no clue about the number of words, but if we can expect them to type 1024 words, we'd still get 20 bits..