After reading Seph'99's post I wanted to add my own thoughts.

FFI (NES) - Yeah, that circle of sages was terrible. Not only were they not very helpful, but when they attempted to tell you about important plot points, they couldn't find a way to do it that made any sense whatsoever. As if that wasn't bad enough, the ending just worsens things by attempting to resolve the logical nightmare caused by said plot points.

FFII (PSX) - The translation was very well done for the most part (ignoring name changes which don't matter too much since you can re-name a few of 'em anyway), but it IS kinda weird that they gave Gus/Guy a speech impediment.

FFIV (IIUS) - Wow. Just WOW. In addition to the line I already gave, there's also the classic "Attacking while mist will freeze with breath!". I won't touch the dumbed down gameplay, since this thread is about the translation, but yes, indeed, this was a thoroughly badly done work.

FFV (PSX) - Didn't really get the chance to play this one on the PSX, but I've seen quite a few funny name changes.

FFVI (IIIUS) - Well it made sense and the English wasn't bad, but a lot of enemy names got changed and censorship was even more prevalent here than in any other FF game. Things were generally made more family friendly.

FFVII (PSX) - You can figure out what's going on, but you might get a headache trying. It's not that incorrect information was given (well, okay, the scorpion boss thing WAS misleading, and there IS no such place as the "knowlespole"), it's just that the grammar was so awkwardly done that it can be hard to tell what's being discussed at times. I'm not even talking about "This man are sick", I'm talking about the general conversation, such as Barret's "That's it! You're comin' with me from now on!"

FFVIII (PSX) - From what I remember, this game had the same weird grammar as FFVII, but without all the terrible glaring errors, such as "Off course!/ No, way!"

As far as the games I didn't list, FFIX-X2 are not games I have completed, so I feel like maybe I shouldn't comment. However, FFIII hasn't even been released here yet *cries*.