I'm not sure that Russian opera is
quite so insular as we might think. Clearly there was a political/cultural element in pre-revolutionary Russian music that was informed by the nationalism so popular across Europe in the nineteenth century but I also think that the success or otherwise of non-Russian/Slavic subjects in opera has been partly affected by what non-Russian audiences/musicologists think Russian music
should sound like. In that respect, it has been common in the past for such works to be dismissed as anomalies or not authentic.
Just off the top of my head, I can think of these non-Russian subjects that were set to music by Russian composers, though not all have been recorded:
Dargomyzhsky:Esmeralda
The Stone Guest
Serov:
Judith
Mussorgsky:Salammbo
Anton Rubinstein:Nero
(The latter perhaps most obviously in the context of this discussion, but also several others including his "sacred operas".)
Rimsky-Korsakov:Mozart and Salieri
Servilia
Tchaikovsky:The Maid of Orleans
Iolanta
Arensky:Raphael
S Taneyev:The Oresteia
Rachmaninov:Francesca da Rimini
Monna Vanna (incomplete).
Ippolitov-Ivanov:Ruth
Cui:William Ratcliffe
Le Flibustier
Angelo
Feast in Time of Plague
Mateo Falcone
plus several others.
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As a postscript for Hattoff, you can find an English libretto for Servilia here -
http://opera.stanford.edu/iu/libretti/servilia.htm :)