I'm not sure - I'm just speculating. That sort of deep cutting (intaglio?) of square vases I remember already seeing in the Art Nouveau period (from companies like Moser and Harrachov). It looks like it sort of follows that tradition, but at a later date. Czech would be my first guess, because of the Svarc impression I get from it, but I wouldn't be surprised if it turned out to be German, Austrian or French even. The base and the opening for the flower look very German for instance.
If it's definitely handcut but relatively modern, I would tend to think it's Czech (or another country were the wages are relatively modest). If it's not handcut but industrially produced it could be French. Like Ivo remarked in another thread, companies like Crystal d'Arques are very good at producing machine made goodlooking vases that look nearly handcut.
And just put your beautiful Riedel vase in the country appropriate discussion forum, Michael, and I'll gladly have a look!
Astrid