TL; DR
Static analysis works by leveraging rules. These rules are grouped by language or language categories in modules that you can install. In addition to providing support for the subsequent languages, these modules can extend the native capabilities of SonarQube.
Most of them are free, some are subject to commercial licenses.
Installing Add-ons
Open SonarQube and go to configuration, system, search for and install the modules that you’re interested in.
Once all the modules installed you need to restart the server using the button available in the UI of SonarQube.