To se mi líbí
During visits to the Czech Republic and also in musical literature I have noticed that the key given during the 18th Century for some pieces (often for wind instruments) is "Dis" (D#). Is this the same as Es (Eb)? If so why is this unusual naming used. It seems to be restricted to the Czech-speaking area. This service was recommended to me by an Australian friend who was very pleased with the help you gave him. It seems to me a wonderful service typical of the respect for knowledge characteristic of Czech culture.
I'm responding to your enquiry concerning keys in music of the 18th century.
The key signature "Dis" (D#) is really the same as "Es" (Eb). I don't think this is unique usage in Czech-speaking areas. These keys were used in 18th century music (not only by composers and copyists from Czech lands) without any special meaning.
Národní knihovna ČR