The TARDIS translation seems to be rather like the Star Trek Universal Translator - it has a built-in mechanism that makes it cut out whenever it's dramatically effective to do so (in ST it's usually when someone wants to show off their Klingon). It's not quite as inconsistent in NuWho as in the classic series, but sometimes the writers seem to forget.
I could see that among different writers, but Moffat wrote both of them! He of all people should have caught that one.
Of course, River does say in AGMGTW that Gallifreyan writing doesn't translate, but there's never been any problem in the past with Time Lords making themselves understood. And there's no reason why the Doctor wouldn't understand it, anyway.
Exactly! The Doctor should have been the ONLY being in the universe who understood the message.