UK boxshot and screenshots are
here if you want to take a better look at the game in its localised form.
Given that there is no NTSC-to-PAL video convesion problems when dealing with handhealds I'm going to assume that the gameplay will remain basically intact. There is always the possibility of them ripping out any speech, replacing the intro song or hacking up any FMV to remove Japanese text, but as they dont seem to be hiding the fact that its a Japanese game this time, and the intro and intro song are already
in english I suspect it'll be left pretty much alone.
Midas previously released Neverland Zero under the name
Realm of the Dead (dig that box-art

) which is part of the same franchise. Despite the re-titling, the intro was left pretty much alone - including the comical j-rock song - and there was (subtitled) japanese speech still left in the game. However a few FMV sequences looked as though they had been hacked short to cut out some Japanese text.
Oh, and the game itself is pretty crap anyway.
Just bear in mind that Midas Interactive are a
budget software publisher, so dont go expecting an Atlus-quality localisation.