The TNG:TM tells us that the Universal Translator super-imposes translated speech over the normal speech (in his/her/its mother-language) of the subject. This would cause the 'bad-lip-sync effect', as I call it. But we don't see evidence of anything such on-screen. (OK, it would be very confusing for the TV watcher, but let's forget this)
My theory is that any Universal Translator also has a holographic projector, maybe working in conjunction with advanced facial scanning techniques, which provides real-time holographic manipulation: a hologram projected over the subject's face, with its lips moving according to English speech (or Federation Standard ).
What do you think?
------------------
Signature.
I say, they do look funny and that's it. I watch Star Trek in Spanish, and they're already lipsync-ed. So for me, it's not big deal
------------------
Is this the real life? Is this just fantasy?
Caught in a landslide, No escape from reality
------------------
"Content, graphics, and design are © 1999-2000 by The Solareclipse Network"
-And no-one even noticed the typo...
---
Titan Fleet Yards - Harry Doddema's Star Trek Site
Another thought occurred to me: holography is not necessary when you're talking to an alien via a viewscreen. Sophisticated software might be installed for real-time video manipulation to get rid of the "out-of-sync" chatter.
Anyway, I think 24th century engineers should have invented something to compensate.
------------------
Signature.