Ok, tried to tweak the install process as described - pausing the PTS installation process in the launcher and transferring all 'vo_(xx)' files (like vo_en, etc.) to the PTS folder. Then chosing the 'repair' option and continuing the PTS download.
Initially, 8% of the total install were verified and the rest downloaded. After the full download I got 'Patch Manifest Error 209'. Followed this troubleshoot:
https://help.elderscrollsonline.com/#de/answer/6487
As a last step it has deleting several 'xx.version' files (like depot.version, etc.), then restarting, and then repairing install. Unfortunately, after deleting just these version files and restarting PC, restarting launcher, clicking repair: the entire PTS installation was gone!
Re-downloaded it from scratch. Now it works.
*Ancient saying from Europe: .. und die Moral von der Geschicht: manche Abkürzungen gibt es nicht.
Still: thank you very much @Baertram for giving it a try! (and regarding your Avatar-pic: that's no winter outfit
)