We hate the translation. Previously, it always had translation on by default; now, it inserts a link into every chat message from a person with a different region, to translate on demand.
Store cookies. Or something. Just let us turn it off completely and remember the setting, please. I'm debating writing another browser extension just to strip that feature, because of the PITA it has been. The rare usefulness nowhere near outweighs the endless, though trivial, battles.
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That aside, it has been handy to have, and works quite slickly. Scroll-back through several hours of history works well. And what can I say: it's a chat tool. It works. It doesn't do much else, and I don't want it to. Good job!
All in all I really do like it. Especially being able to pop chats out into other windows. That, and the scroll-back, make it absolutely one of the better ones I've used, and nearly everything it does has been useful at one time or another. It gets used heavily, and there hasn't been one word of setting up a different system (eg, IRC) that I've ever seen. The translator's behavior is just a burr on an otherwise good finish :)
edit: a thought; maybe you could come up with a language detector, to ditch false positives (by default; having an override is nice, and I liked the click-to-toggle)? Certain letter combinations don't appear in some languages, some accented characters, that sort of thing. Or have you looked at Google's language detecting API? No clue how they respond to volume.