So, after a few hours with the US release of FFXIII (and significantly more time with the import) thought I'd do a bit of a writeup for the differences in localization, for people interested in that aspect of the industry or just plain curious how the US release shaped up to the Japanese release.  Obviously, this is mostly gonna be focused on voicework and the translations.   If you're apathetic or have no interest in ever checking out the Japanese version, you can probably skip this. 
 
Technical Considerations 
None, everything on the US PS3 release runs just as smoothly as the Japanese PS3 release.  I can't speak for the 360 version, but if people really care I can borrow a friend's to test that too.  I'm sure somebody else will have plenty to say on this though.
  
Music
No surprise here that the music is about the same, worth noting that there is a major song difference (They use Lenoa Lewis's "My Hands" instead of "Kimi ga Iru Kara"  by Sugawara Sayuri).  Personally, I immensely prefer Kimi ga Iru Kara, since one was prepared for the game and the other wasn't.  It just feels a lot more relevant to me overall.  I wish they had used the precedent they set in FFX of just including the original Japanese track.   
 
Translation 
Very solid, I'd expect nothing less from Square.  Since this isn't a game that is based heavily on Japanese culture, they didn't really have to change anything (like in Shin Megami Tensei games) so the translation is basically direct.  I think some of Vanille's best mannerisms are lost in the translation, but there's no real way to write her dialogue appropriately in a language besides Japanese. 
 
Voice Acting 
 Aa, here is the rub, and where the two versions are gonna differ a lot.  I was really hoping that we'd get a Japanese language track option with the extra 12 GB of space they had leftover on the disc, but no such luck.  The minor characters are all about what you'd expect, and they are minor enough that the quality doesn't really matter.  You may hear some familiar voices in the English version though, some familiar VAs such as Tidus's will make returns.  
 
Lightning - I think she does well, the character doesn't have a lot of heavy speaking roles early in the game, but the English voice actor seems to play the role about as you'd expect.  I'd rate the two versions about the same here. 
Sazh - I think the English voice actor does an AMAZING job with Sazh, and I actually find myself liking him a lot more than the Japanese Sazh.  Clear win for the English localization here.   
Snow - Also good, I'd say he ranks about the same as Lightning.  The voice actor takes a bit of a different approach to him, but does a good job still.  I find myself liking him about the same as I did in the Japanese voice. 
Hope - The Japanese Hope sounded like a guy in his 30s trying to sound twelve.  The English hope sounds like a 12 year old trying to sound a bit older.  Both of them are immensely annoying, and I can't stand either one.  I guess the English one is a bit better and fits the character more, but the character is still incredibly annoying. 
Vanille - Unfortunately, this is a character that just can't work in any language but Japanese or maybe Mandarin.  'Cute Japanese girl speak' just doesn't work in English, and it is always painful to see people try to do it.  Double that with an Australian voice actress who can't tell if she wants to embrace her Australian accent or hide it, and it comes off as probably the worst voice job in the localization.  Sometimes I dug it, and sometimes it just sounded painful.  I think she should have just embraced the Australian accent full force (aussie accents are great), and not tried so hard to be Japanese.  One of my favourite characters from the original Japanese, and she just comes across as really awkward in English. 
 
Overall Opinion: A- 
Great localization, in some areas it even surpassed the original (Sazh and arguably Hope).  A few disappointments here and there (change of Japanese theme music and Vanille's voice actor) but an overall shining job for localization, and if there were people on the fence about which version to play, the US version is totally okay.  Though if you were holding out before, you probably already imported the Japanese release.   
 
I can't get rid of the random underline in the Music section, sorry.

In terms of Vanille: 
"Moe" never fits in any language sans Japanese. Even in Haruhi, whoever did the official dub couldn't capture Mikuru. 
 
However, what annoys me is the report of a half-done accent. I would just have preferred that she kept it like Fang did in the trailer [same in-game/real country...?], but beggars can't be choosers. 
  
In other terms: 
Sounds like a typical English dub...only except this time slandering the music and not the voices.

Well, done properly I don't mind the music change.  FFX-2 it made sense, since 1000 Words was very relevant to the story, and they actually made an English version specifically for the game.  Same for SImple and Clean vs Hikari in KH (Especially since it was the same artist). 
 
It's odd in XIII, because they just take a song that already existed and put it in place of a song that was more appropriate for the circumstances.

Shame about Vanille. I got a glimpse of that... character in the gametrailers review, and what I saw there was horrifying. 
 
If there is a character whose voice and mannerisms are a defining characteristic that cannot be translated, either A) don't try or B) replace it with something that works and is approriatly "distinguishing" in the target language. 
 
A bit of trivia: The German translator of Final Fantasy IX actually did this on a major scale. As far as I understood, there are lots and lots of different speaking patterns and mannerisms in the japanese original text - in the localized German version, every character is very carefully realized with a spot-on accent (such as bavarian, saxony) or unique way of speaking. The translation was very positively received and praised. The translator claims to have played through the japanese version twice before even starting the translation.

" Well, done properly I don't mind the music change.  FFX-2 it made sense, since 1000 Words was very relevant to the story, and they actually made an English version specifically for the game.  Same for SImple and Clean vs Hikari in KH (Especially since it was the same artist).  It's odd in XIII, because they just take a song that already existed and put it in place of a song that was more appropriate for the circumstances. "

"  @Aus_azn:  Yeah, I'm a big fan of Hikki as well, saw her in concert when she went to NYC, was fantastic.  

Good post, thanks. I'm still on the fence about whether or not to pick up the english version. I loved the import copy but I don't see myself paying full price just to fill in some of the plot details I missed playing in Japanese. 
 
I completely agree with you about the music. It's a shame really, Kimi Ga Iru Kara is such a great song and fits the game perfectly. It makes little sense to dump it in favor of a western song chosen seemingly at random.

I'd say it's not necessary to play the US release if you have played the Japanese version and understood it pretty well.  There were parts in the datalogue I didn't quite follow in Japanese (Curse you kanji), but so far they don't seem to be hugely important either.  That said, I really do like the American Sazh voce actor (Reno Wilson apparently, hasn't done a whole lot of VA but should probably do more of it).