I have a very specific question, which I have not been able to find the solution

I want to search Superuser and other websites using Google, but I want to limit it to a specific subject (e.g. the R programming language). Using Superuser paths for specific topics like

"site:http://superuser.com/questions/tagged/r"

Does not work, as can be seen when comparing searching using full path compared to searching entire website with more specific question. Also note the first hit being one step in the direction i want, but since this path itself does not hold the questions in its path it does not solve my issue.

There should however be a better way to do this, e.g. by having a very specific Google search tag for the R programming language, which would have to be either in the path, on the webpage, or tagged differently. Seeing as Superuser has a good tag system I am optimistic that this can be used to solve my question.

Is there a solution to this that always works on Superuser and similar sites?