Here are things that still can't be translated in-game till today. Found in 100% translated(as the google doc says) language.
Main Menu buttons & Editor buttons
Seems like they are pictures instead of strings. I've heard that osu!next is on the way, please consider making translating these possible in next generation osu!.
Song Setup / Timing Panel
These look easier to translate comparing to first one.
Sampleset / Additions
By the way, the
Normal in the list seemed to be cut off.
User Panel
Maybe
Performance and
Accuracy can use translations. And
the states of player, for example: Idle, Playing, Watching...
Key Binding
Might help those players who don't understand English very much if they're translated.
Music Player Description
Those buttons tell what they do from what they look, but if they're translated the whole experience will be better in other languages. Or just say I am picky. Both ways can do. Don't forget the
All in Jump to window, and the messages showing up when player used one of the shortcut keys.
Making a room / Changing the password / Winning Conditions / Team Modes
Also the
Creating room... or something like that message. Maybe the
Stars can be translated, too?
!help Description
Some of these commands, including !where and !stats, are frequently used even by normal users. Maybe you can concern adding description for them, if they can't be translated? Since it looks like this works in a different way than /help.
#Announce announces
As above, if they can't be translated then so be it
Checking messages when exiting osu!
Addfriend message / delfriend message[/img]
[heading]Names of map groups
No matter which grouping way you use, these folders' names are all untranslated.
Disabling / Enabling Mouse through F10 message
Ignoring message(Bancho)
Somehow unignoring messages are translated.
Also, these c/h/p things can't be translated.
Cinema Mod
It has no description, though. Cinema deserves a description!
+Set
Not so vital, though.