Is a UK PAL video tape compatible with a continental Europe PAL VHS/S-VHS player in terms of video and sound
The UK PAL VHS tapes will play back in a German PAL deck. The actual method of audio recording is not related to the PAL specification. VHS records up to two linear audio tracks. HiFi capable decks record additional two HiFi tracks that are  multiplexed with the video signal. I don't remember the details.

A non-HiFi deck will ignore the HiFi tracks and use the linear tracks which should have the same content recorded.