When closing a question as off topic the first option says:

Your question should be specific to WordPress. Generic PHP/JS/SQL/HTML/CSS questions might be better asked at Stack Overflow or another appropriate Stack Exchange network site. Third party plugins and themes are off topic, they are better asked about at their developers' support routes.

I want to propose a different wording for the first sentence, to make more clear what we mean by "WordPress":

Your question should be about development issues with the Core of WordPress.

The other two sentences are pretty long and may be confusing to users who are less familiar with the english language. So I propose this:

Specific plugins and themes are not part of Core. Ask about them on their authors' forum. Questions about PHP/JS/SQL/HTML/CSS in general are better asked at Stack Overflow.

When closing a question as off topic the first option says:

Your question should be specific to WordPress. Generic PHP/JS/SQL/HTML/CSS questions might be better asked at Stack Overflow or another appropriate Stack Exchange network site. Third party plugins and themes are off topic, they are better asked about at their developers' support routes.

I want to propose a different wording for the first sentence, to make more clear what we mean by "WordPress":

Your question should be about development issues with the Core of WordPress.

The other two sentences are pretty long and may be confusing to users who are less familiar with the english language. So I propose this:

Specific plugins and themes are not part of Core. Ask about them on their authors' forum. Questions about PHP/JS/SQL/HTML/CSS in general are better asked at Stack Overflow.

update

How about this:

Your question should be about development issues with WordPress proper. Third party plugins/themes usually have their own forum, dedicated to your questions about them. StackOverflow is the best place for generic PHP/JS/SQL/HTML/CSS questions.