Can we draw the following hypothesis from the context? 

Context:

Silvana, J. 87, is an opera by Carl Maria von Weber, first performed in Frankfurt am Main on 16 September 1810. The libretto, by , is a reworking of an earlier, unsuccessful opera by Weber, "Das Waldmädchen ". Weber also reused music from the same piece in "Silvana".

Hypothesis: Silvana, J. 87 is performed in German.
It's impossible to say