Actually, scrap all of my previous answers.  The two games I wanted localized most were these two:

Robbit Mon Dieu (aka Jumping Flash! 3) and Ape Escape Big Mission.

The former I played on a friend's imported PS1.  The latter I actually imported myself when I got my PSP because I wanted to play it that much.

Both excellent games that I would've enjoyed more if they were in English.

NEW LOVE PLUS +

I hope it has not only localisation, but aslo a NA version of limited 3DS XL console

My most wanted localization was solved by Dejap over a decade ago with Tales of Phantasia and Seiken 3.

Tales of Vesperia PS3.

Mother and Mother 3.

If we're talking about now, Dragon Quest VII and X really need to get localized. I can't wait to play both of these games.

If we're talking about all time, I would say Mother 3 (even though it has a fan translation out there) and Custom Robo 1 & 2 for the N64 because I love the Custom Robo series.

Speaking of Mother 3, does anybody remember the miiverse page called Onett Times Nintendo set up? Whatever happened to that?

PSO for Vita

Those Tales of games for the Vita.

Phoenix Wright vs Professor Layton