Haven't heard of anyone testing it, but if the only difference between the versions if the amount of characters, English might be the fastest. German at least is known to have a lot of letters, Italian, Spanish and French I don't think are significantly shorter. Feel free to test it out yourself, start of Disc 3 is probably the longest section of text and minimal movement so I guess that would be a good place to test it.
Language in this game doesn't make an awful lot of difference because text appears instantly and you're only changing the size of the text box. The boxes still have to 'grow' and 'shrink' to different sizes to fit different text so you can still save a frame or two on a text box, but it's much less significant than other games. I'd be surprised if it amounted to anything more than like 5 seconds.
