[...] It is true that I have to face the fact that I have been obliged to lay out even more than the sum received from you to meet the really enormous expenses of the three concerts I have given, and yet I may consider my immediate object fully attained, since I have every reason to be satisfied with the impression made by my music on the Parisian public, and there can be no question but that the result will be the dissemination of my work through the length and breadth of France. [...]
I am quite definitely opposed to your project for including French words from the first in the pianoforte arrangement of The Rhinegold. I know the uncommon difficulty of getting a really good translation of my operas, and can only hope for an entirely successful one if I myself alter and adapt the voice parts to make them fit in quite naturally with the demands of French declamation. While reserving to myself this necessary freedom, I must also ask you at the same time for a special edition with the French libretto, since this is no mere question of giving the words in two languages but very frequently of entirely altering the notes of a song. To include both versions in one edition would necessarily lead to such disfigurement of the voice parts, that neither Frenchman nor German could easily read them, and in any case the whole would have an unsightly and muddled appearance.
This consideration would, perhaps, apply less to the full score, as this will come far less into the hands of the general public. [...]
In any case I must look over the full score again. I hope to find a means of indicating to less well-equipped theatres how the orchestra I had originally in mind might be reduced to come within the scope of the resources ordinarily at their command. [...]
Source: Letters of Richard Wagner, Vol. 2, selected and ed. Wilhelm Altmann, trans. M. M. Bozman (J. M. Dent & Sons, 1927), No. 457