Custom voice acting in games.

[Vag]

Custom voice acting is quite hard to do, and I've personally not seen (yet) any fan made translation of any game's voices, just texts, exactly because it's quite a major task.

There's going to be one, soon - or not so soon (in Greek).
The sound files of FOTAQ can be corresponded to the phrases in the game. The text itself has some control characters for animation and other things, together with the delay. So any lip sync issues can be solved.

[dj jack]

Major bump for a very old thread BUT it looks like somebody actually had my same idea some time ago...

ScummSpeaks: a tool that lets you add voice acting to the mighty Monkey Island 2 + ScummVM combo...

[LogicDeLuxe]

but what about on-the-fly created lines? Like saying "I have <number of coins> coins in my inventory", where the number is inserted into the appropriate position?

There is actually an example in Sam&Max: Try picking up some random items which can't be picked up several times. Watch the subtitles! Eventually, Sam tells you the item ID. Of course, this is in the subtitle only, but not in the voice acting.

Thinking of the Monkey Island games, there are cases where numbers aren't really important to be spoken. In case of coins, the bottle of grog and the rope in the Monkey Island games, the inventory text petty much tells you what you need to know.
In the other hand, there are cases where this is essentially to advance in the game: The coordinates of the figurehead you read up in the book (Guybrush reads in the form of subtitles) is one of them.
Also important is the number you get for the wheel of fortune.

Another problem are lines which are used by more than one actor. Most notably in the sword fight dialogs. Also almost anything in Maniac Mansion.

The number of pieces of eight you can have is actually only very limited

You can put any amount of coins in the grog machine, so you can have any number between what you get from the fetuchini brothers + those 2 you get with the agenda down to 0.
In Monkey 2, Guybrush just says "I'm rich." which could be easily used in Monkey 1 as well.

[jestar_jokin]

If you're willing to get your hands dirty, you could hack the scripts to suit your needs. I've made a text-to-speech proof of concept for Monkey Island 2:

http://www.youtube.com/watch?v=M92Af7HUzok

Although it's not really necessary for that scene, it could be useful for situtations like the "x bottles of beer on the wall" song.

[Arantor]

And in MI2 it's possible to have a very varied number of pieces of eight since you can polish the peg leg of the dude from the Men of Low Moral Fibre, and he'll give you one piece of eight...