Ok, we know that the TARDIS does the translation work for the Doctor and his companion, so they can understand what other aliens say. It does that basically by using telepathy. But how does it translate back - meaning, how can those aliens understand what the Doctor or his companion says (since apparently they are speaking English)? Does the TARDIS translate for them too?
Basically, the TARDIS converts what The Doctor and his companions speak to the language of the aliens they are talking to. And similarly, it captures what the aliens say, and translates it to English so that The Doctor and companions may understand it. It doesn't cause the aliens to speak English. It causes The Doctor and companions to understand them. So as far as your question goes, it doesn't translate what the aliens say, it translates what The Doctor and companions say.
1.The christmas invasion
The humans suddenly start understanding the Sycorax in The christmas invasion. When they ask how the Sycorax are speaking English, the Sycorax leader angrily replies that he is speaking in his native language.
2.The rings of Akhaten
The Doctor is perfectly able to understand and speak to the Dor'een whom he later rents the flying machine from.
This gives us a good idea as to how the translation process works.
There's some debate on whether the Doctor is actually speaking the different languages because he CAN speak them, or whether the TARDIS is doing the work for him, but often it is assumed that the TARDIS has the ability to access the minds of aliens as well as the Doctor and his companion. The aliens aren't aware of it, but they are having what the Doctor and his companion say translated for them into their own language, and what they say back is translated into the native language of the companion and the Doctor. It's a mutual exchange.