One of the gaps in my knowledge of Russian literature has long been Tyutchev, universally considered one of the three great Russian poets of the Romantic generation (alongside Pushkin and Lermontov). Now that I have a collection of his poetry (thanks, Jim!) I’m trying to remedy that, and to get some background I turned to my favorite source for the nineteenth century, D. S. Mirsky’s A History of Russian Literature. There, after a description of his unusual career (joined the foreign service at 18; spent most of the next 22 years in Munich, which he considered his home; married two Bavarian women in succession; returned to Russia and became a reactionary polemicist), I found this astonishing paragraph:
From the linguistic point of view Tyutchev is a curious phenomenon. In private and public life he spoke and wrote nothing but French. All his letters, all his political writings, are in that language, as well as all his reported witticisms. Neither his first nor his second wife spoke Russian. He does not seem to have used Russian except for poetical purposes. His few French poems, on the other hand, though interesting, are for the most part trifles and give no hint of the great poet he was in Russian.
I know of no other case of a great poet who used the language of his poetry only for that purpose.