Even as a child, I was amazed by the concept of the Babelfish in the book 'The Hitchikers Guide to the Galaxy' and wondered if it can be done (scaled down to world languages. Imagine a DS that you speak into in, for example, English and when you hit a button (or just stop speaking) it then speaks in the destination language, for example Japanese.
Internally I think this:
Speech -> Text ->Translate->Phonetic Text->Speech
I suggest that it would be cool to use the internet Babelfish as a backbone and then add a nice ST->TS front end.
Now, I imagine everyone is concerned with all the mistakes it is bound to make, right? Here we need a lot of training. A website with a PC version of Babelfish would allow users from all over the world to train the ST element many, many times (of course you can train on all platforms, but the PC is likely the easiest).
Lets assume the DS platform with a cartridge with a LOT of SRAM or such to store all the training data. You train the software with your voice and your inflections and then download that. Now your DS version gets better. Repeat & refine until it correctly converts huge slabs of speech without a hiccup.
This would be an interesting product since the makers cannot control just what is in the product. Of course, there would be websites with training data and for each language, a group of users could tackle a language...
Just a thought, but wouldn't it be nice to be able to speak phrase Japanese just by speaking into your DS and hitting a button?
Extras? Well, placenames and such cannot be directly translate but maybe the software can do a first-pass to spot untranslatable words and asks if they are proper names. Not good in a real situation, but again it could be trained to spot untranslatable content in advance so food, places, peoples names can be added before you visit...
It would have a LOOONNNGGG product cycle but it would get better and better. Oh, to help with untranslatable things, it could bring up images or play sounds or rumble or whatever to get the point across.
No more asking each other the way to the beach in loud voices ;-)