Assuming it is accepted and merged, the new verbiage will be in the next release of the npp-user-manual.org website, which will likely happen soon after the next version of Notepad++ is released.

Until it is merged, there is still time for further clarification if people wanted to comment on the chosen wording/explanation.

But I don’t understand why in C the commentblock with …
works after all?
And in Lisp …
works not.

Because, as @ArkadiuszMichalski already said, the commentLine, commentStart, and commentEnd attributes in the langs.xml are only used by the “toggle line/block comments” – which means for the Edit > Comment/Uncomment menu actions:

The syntax highlighting is handled by a library of compiled C++ “lexer” code inside Notepad++; the lexer for C/C++ knows that /* ... */ is a block comment and // is a line comment; the lexer for LISP believes that #|comment|# is the block-comment syntax for LISP. The LISP lexer does not look at the XML attributes mentioned above when deciding what is and is not a comment, and you cannot change what the lexer considers a comment by changing those attributes in the langs.xml config file.

If the LISP lexer implementation is wrong, then it would have to be proven wrong in the original Scintilla library implementation, then a bug reported to Scintilla (which is a completely separate project, which the Notepad++ developers have no influence over), then they would have to decide to fix it, and release a new version of the Scintilla library, and then Notepad++ developers would have to incorporate that newer version into the Notepad++ codebase. If it happened at all, it would be a long process. (And you would have to check; Scintilla has gone through quite a few versions since the last time Notepad++ updated, so maybe the Scintilla LISP lexer already has the updates you desire.)

However, if you wanted a workaround until such time as Notepad++ officially considers those extra LISP notations to be comments, you can add extra highlighting to a builtin lexer (like the LISP lexer) using regexes via the PythonScript plugin in conjunction with the script EnhanceAnyLexer.py that @Ekopalypse shares in his github repo: install PythonScript plugin using the Plugins Admin, install the script per the instructions embedded in the downloaded EnhanceAnyLexer.py file; follow the instructions in that script for customizing it with a regex to match your desired line comments – something like r';\|.*?\|;' as the regex to match (where the backslashes are necessary because regex engine thinks | means LOGICAL-OR, not the literal | character).

Ok, now I understand @Arkadiusz-Michalski’s answer.
For whatever reason, LISP and three other lexers were in the disabled languages box for me and so I didn’t see them when I checked the lexers via the languages menu, which led me to believe it was a UDL issue, which it clearly is not.
Sorry for the confusion.
The LISP lexer only considers |# for comment blocks.

@ ArkadiuszMichalski
I know that the color are made by lexer … strange is, that only “COMMENTLINE” and “COMMENT” is available in lexer. Here “COMMENT” can only mean the commentblock. Or?

But I don’t understand why in C the commentblock with …
commentStart= “/" commentEnd="/”
works after all?
And in Lisp …
commentStart= “;|” commentEnd=“|;”
works not.
Strangely laborious.

I would try to define both in comment style, e.g.

open: ;| ;
close: |; ((EOL))