The DS and other handheld devices strike me as being more suitable for phrasebook type products where you want to look up a specific word or sentences when you're out and about.  Because of the screen size and the lack of multimedia facilities on the DS, I'm not sure this format is totally suitable for complete language learning.

I have used the Berlitz language learning software on PC and I think a DS product could complement this for vocab learning, phrase revision etc when I can't get to a PC.

I recently downloaded a french phrasebook iphone app and I have to say it is excellent. You simply type in the sentence you want to say in English and up pops the french translation. Its perfect when you are in, for instance, a restaurant and you cannot for the life of you remember what french is for "wea ready to order".  Now of course I dont suppose the translation is always that brilliant but however bad it is it will never be as bad as my french accent!

Thanks Debbie for your answer.

@Dave: next time you come to Paris don't forget to come and speak some French with me then!