I have tried quotes. First using my iPad which modified the leading quotes to the lower line (usually like it is used in German writing). This was excepted but as already stated did not work. Today if have tried the same using Firefox on my iMac. Here both quotes had been "top" aligned. In this case I got an error message:
TypeError: array_keys(): Argument #1 ($array) must be of type array, false given
An unforeseen error has occured. This is most likely a bug somewhere.
More info has been written to the DokuWiki error log.
If have only used lower case letters to avoid all problems and of course ":" for the delimiter.
Therefore the only two methods which will work are to enter for example: "..doku.php?id=upper:lower" into the address bar of the browser or as also proposed to enter the desire path into the start page like "[[try:this]]". That's very annoying, but probably my only way out.
Nevertheless, thanks for helping me.