A Prototype / Demo of Pokemon Silver localised for Germany has been preserved and released. This Pokemon Silver demo was purchased from a collector who was selling off various Pokemon prototype carts.
The game was already out in Japan by that time, so don't expect anything major like the space world demos with that in mind, however their are a few minor differences which are explained in the Pokemon Silver German Prototype / Demo release thread.
Regardless it is still indeed a very interesting and very rare release that is now preserved for historical Pokemon preservation.
Thanks to @Deoxyz who made this release possible before he retired from Pokemon related projects.