Translation of Docs in english for Visa

Hi,
My mother in law in filling for visitor visa, she is dependent on her husband. She is showing her husband property Land docs but these docs are not in English they are Indian Regional language (Bengali).....What is the criteria of translation? Can an individual translate it in English and give his details .(Addrs & Ph #) below the documents stating that this is True.

Or there are some specialist for translation of docs. I have read UKBA website it is not clear..please clarify.
Many thnks

Normally any documents which are not in English have to be translated and certified.

I have seen an exceptions, though - clients applying from Spain did not have to do that as the UK Visa Section staff were speaking Spanish there.