I am seeking recommendations for a high-quality chat software product that will allow for

•Moderated discussions with a guest speaker
•At least 100 participants in the room
•If possible, contain a translation feature so that users can read the chat in any language.

I have looked at Parachat and Volano (neither of which has the translation feature) and am currently most interested in Parachat. We are not interested in free programs for a variety of reasons that I will not list here. Recommendations would be greatly appreciated.

I use chat4all, which is an IRC script. Not sure if it'll do everything you want, but it works well. Take a look at their features.