Traducció - Francès-Anglès - Ont mieux montré ce qu'il y avait de vrai en cette...

How about "have better shown what is real in this work of art ..."?

It does sound much better, Kafetzou
The only problem I have is the distinction between "real" and "true" which, well, in some circumstances can be two very different concepts. The original does not use "réél", but then I don't know if it means much...
Tough...

How about "what is true" then?

Also, what about "its principles"? Only a person or an institution can have principles in English, not a work of art.

"Principes" also sounds a little weird in French, but, like in French, I'm not sure the use of the word "principle" is that restricted. I'm thinking of the meaning of "laws underlying the way in which a particular object works" and that object does not need to be thinking or alive or made up of a thinking body (as in the case of an institution), as these "principles" are applied to it, not inherent to it. The simple meaning of "origin" could account for a use of the word, too.
This is yet another example of how impossible it is to give definite answers without proper context ( I mean... this sentence doesn't even have a subject! )

Good points all. I decided to accept your translation as is.