Is it possible to use a modern, digital flash (like the Metz 36 AF-5) on an analog film SLR?
I know that I have to be careful if I use it the other way around (old flash + DSLR) because of high trigger voltages, but will the Metz even fire when used on the Praktica?
Maybe. The answer to your question is model specific for each camera and flash in question. Without knowing exactly which film SLR you are interested in, it is impossible to say for sure. It all depends on whether the trigger voltage for the flash and the trigger voltage for the camera are in the same range or not.
The Metz website lists the model 50 AF-1 and 58 AF-2 as compatible with the Canon EOS 1, but not older models like the A-1 and AL-1. The same search tool also shows the Metz 50 AF-1 and 58 AF-2 models as compatible with many Nikon film cameras.