A friend who speaks the language is unlikely to be accepted as a translation. Either use a teacher or another official source.
And should I inform them that the letter was translated?
I payed 20€ to get a document translated. They used to do it at the british council but they stopped having any translation/counselling services some years ago. Apparently "all the info is on our website". They gave the some contacts of people who used to work there though, I called some of them up, and it was quite easy, apart from the fact that it was summer and all except one actually answered me. I e-mailed a scan of the document and got a translation 2 hours later I guess, with the "oh look I got fired but I still have the whole stamp and signature thing so I'll always look professional" going on.
I thought about going to the British council. I’ll have to look into it and if I’m not as lucky as you I’ll ask one my teachers to forward the letters to one of the English teachers to translate it then send it back to my teachers for them to send to UCAS…