Hi, I'm teaching English in China to professors with good vocabularies but who are still working on pronunciation and grammar.
Each afternoon we gather in a group of 30 and play various language related games, such as a version of team Scattergories. I'm looking for other group games that encourage conversation and don't require a physical boardgame, although I can certainly purchase supplies and assemble some items.
The Three Things Game is a party game based on Celebrities. It's played in three rounds, and two of the rounds involve language. The third involves movements but no speaking or other sounds. I have played it with about 20 people, and it was still pretty good. You definitely need at least 6 for it to be fun. And I guess you would add a rule that all speaking during the game must be in English. http://www.boardgamegeek.com/filepage/36560/three-things-a-c...
With a group of that size, I used to put 2 free standing black-boards in the center of the room....one team on each side and then play a version of pictionary. Both teams are given the same word and draw at the same time....but you can only see your team's drawing. It was fun.
Wits & Wagers is a potential but I would hand pick the questions and extend the timer due to everyone probably being a tad slower getting their point across. I've played it with teams of two but three in a group could work.