It's time to summarize our discussion.
First of all, the original idea was orthodox.
Against:
costs a lot
hard to play (a few would play without on/off switch)
a lot of time to prepare
how to reproduce speech of some "dead" languages
For:
learns languages
funny
adds gameplay
increases realism
I think that most of us will support this idea: speech in native language and its translation in english, plus "in game" text in english.
This one is better because can be easily implemented, and adds no difficulty to play.
I want it implemented in Civ4
And what with customized Civs? Simply create your soundtrack...
Another idea from RTS world. Give each type of unit unique speech or sound. When you select a unit or give him an order it will say something.
Anyone for... against...