It has never been stated explicitly whether or not TARDIS translation can be switched off. However, in "The Stolen Earth", when the Tenth Doctor took Donna to the Shadow Proclamation, the translation seemed not to be working. The Doctor spoke to the Judoon in their own language & Donna didn't appear to understand the conversation (which she would have, if it had been translated for her).
On other occasions when the translation hasn't worked, a reason has been supplied:
- In "The Impossible Planet", the Doctor said the writing was too old to be translated.
- In "The Christmas Invasion", the Doctor was unconscious because of regeneration trauma & translation resumed as soon as he recovered (as Rose realised).
- In "Planet of the Dead", the TARDIS was absent (still on Earth).
- In "A Good Man Goes to War", the language was Gallifreyan & River explained that it "doesn't translate".
Without an explanation & just going by what was shown in "The Stolen Earth", we can't tell if the translation had been switched off or if there was something either about the Shadow Proclamation in general or about the Judoon specifically that prevented it from working. The translation did appear to be working shortly thereafter, when the Doctor & Donna were speaking to the Shadow Architect.