Re: Mutah [temporary marriage] – Social and cultural perspective
The whole scene is in enlglish, so out all the people here i suspect you should be the last person who wont get it 
Briefly. The reference to mutah is not about its validity, but the brilliance with which the scene is shot and acted. while watching you will note that weston, though being a british soldier, has a soft corner for this society, culture and people. and he admires the king 's (nawab Salamat ali ) poetry and love for art. So he is presenting king’s image in a positive vein. Thus when commanding officer deduce meaning that Mutah as ‘temporary’
but wesston reluctantly tells him the real meaning.
Through this whole conversation the director has told us how deeply and accurately British folks used to investigate a particular society and cultures before invading it, one of the reasons of the huge success rate.