I came back to play after a long time and I'm happy to see here a post about localization.
I've noticed many inconsistencies in the italian version, which I'm going to fix, so I hope you are still accepting changes.
There are some linguistic mistakes (if you translate invalid->invalido you are probably talking about somebody on a wheel chair instead of a not valid format XD), and grammatical mistakes ("un" maschile va senza apostrofo!), but most mistakes regard only mispelling and typing (such as double letters, missing punctuation and capital letters), while there are some sentences that even though correct don't sound really good, probably because the translators have focused on literally translating the message, which of course does not always work out good.
Problems like these inevitably occur when you only look at the written text outside of the context, so that's why I'll have to ask some questions, and I hope that somebody will help. :-)
1) AICompose_ObjectEndOffscreen: Object's end is offscreen! - by "end" you mean its extremity?
2) By "Spinners must have a new combo." (line 17), you mean that there should be a new combo following the spinner?
3) What does it mean: "Artist conflicts with {0} diff."?
4) as above: "Unicode Artist"
5) as above: "Romanised artist" <- has it something to do with the japanese writing conversion?
6) "Kiai time is toggled on for less than 15 seconds." (line 71) means that it should stay active for more?
7) In which context is Editor_Design_Failing used?
8) Editor_FileOperations_SubmitDialog_2: You must place beats before submitting... - what does "beats" refer to? Right now it is translated as "notes", but I thought it could be referred to the pulsing beat given by the rhythm. *For italian speakers: what do you think about "battuta"?*
9) About suspension points and other punctuation marks: the use of punctuation marks differs from language to language, and I've seen that in english sentences you use them... a lot! Imho there is no need to keep them in the italian translation in all the cases (just in some, for instance "rotate by..." would be with the dots also in italian, but complete sentences like "move all elements in time..." would not).
More questions to come as I move forward in the text. :-)
P.S. I'm sorry if I seem pedant, but I think this game has reached such standards that it cannot afford sloppy translations anymore, and plus playing without having to blink at grammatical errors is good for your score and your mental health. ;-)