I can win any game of 20 questions. Not that it'd be very much fun.

The English language, there are around 250,000 common words, and less than a million even by the most generous counts.

One could phrase every question in a game of twenty questions into the form “Does the answer come before … in the dictionary?” Thus using a dichotomic divide and conquer search algorithm, come up with the answer. Very worst case scenario, given a quarter-million known possibilities is 19 (log_2(250,000) + 1) questions, so there's even a bit of room for error!