OK this is really only for language nerds but..

when I was learning the German language I bought the German version of Oblivion (which I had already played in my native English) and found it a really useful tool. If you point your character at an apple, for example, it will display the word Apfel, really good for picking up day-to-day objects. Working out accurately what a quest giver is instructing you to do becomes a really rewarding language puzzle, and you can take it as slow as you like to pick it up. It was awesome, and contributed a really interesting element to the game which is hard to describe.

So I propose a mod in which the sound files from different language versions of Skyrim are switched around so that different holds/races speak in a different tongue. The subtitles can be switched between all versions (so you can read in English, Spanish, Japanese, whatever). This way the PC would encounter a variety of languages in their journey, and need to learn enough of each to participate in all the cultures.

Now the hard bit:

Which language for which race?

language per race is interessant, but per region is more.
if I receive money to create sound files in portuguese, and subtitles: sure, I'm in.

but, do this for free?
nerdy ideas svcks if you have a real life.

One major issue here. Most Bethesda games are single language only, dependant on the country you live in and the version you buy.

However, to make this mod you'd need to distribute the files- the language/sound files- that came with the game, so people could obtain them to make the mod work.

However.

Distributing any main game files is considered piracy. Hence, thats your biggest issue,

Khajiit: Ta'agra
http://www.youtube.com/watch?v=6mMNZ7G0cBI&feature=player_detailpage#t=300s

;)

The idea sounds nice for the purpose of learning languages, and might be possible, when steam allows language-change.

But for normal gameplay to showcase racial differences, made-up languages with sub-titles work just as well, IMO, and you can avoid the limited-dialogue due to voice acting issue that way.