Spell-as-you-type language recognition

Hi

I'm thinking of implementing a new feature in kmail but I'm unsure of where to 
start. 

The feature as I see it:
* A user can choose more than one languages that are usually used. 
* The spell-as-you type should try to guess what language is used by choosing 
the dicitionary that gives the smallest amount of errors.
* It might be possible to mix two languages. As is often the case in for 
example a bug report some parts are in my native language and some in 
english. In that case it would be preferable to use two languages. 
* There should also be some status indicator that shows what language is 
identified and it should be possible to overrun this feature. 

Question about this feature:
* Does it already exist?
* Where should it go?  (KMail, KDE, aspell/ispell)
* Is it interesting?

Regards Per Öberg