Siliconera reports that the English version of Kingdom Hearts 358/2 Days will arrive in Europe later this year, though it should be noted there isn't any official source on the matter. We trust those guys, but, without a source, this has to be treated as a rumor.
Right now, the current release date for North America is whenever, though it's a safe bet to assume the game will be here within the same timeframe as Europe (sometime between September and November), as Square Enix is notorious for releasing its games only days apart in the European and North American regions. Of course, that would only happen if this rumor pans out, and we've contacted Square Enix to clarify and we'll be sure to update you as soon as we have official word.
Kingdom Hearts 358/2 Days will release in Japan on Sunday, May 30.