This is to accommodate the languages with longer text strings. The European version adds a thinner font which is typically used in windows without much space. This was bumped up to six in the other versions. The Japanese Final Fantasy still limits names to four characters.
The European version also updates the deceptively-named 'B Button Dash' option to 'Run Mode', since the option toggles whether or not to always run, and has nothing to do with the B button dash ability. Since the US version lacks this option, the other options in the config menu have been padded out to better fill in the empty space. In either version, this option can later be changed in the config menu. The English script was actually updated for this version, mostly to change American spelling to British, but some other changes were also made, such as Garland's infamous 'knock you all down' quote, which was changed to 'cut you down to size'. A similar menu is shown upon starting the European version for the first time, allowing you to select which of the five supported languages you want to play the game in.