How to develop plugin for Intellij Ultimate version?

How can I develop a plugin for language which is not supported by Community version, for e.g. Javascript? 

Can I extend the language in plugin.xml just like this?

<psi.referenceContributor language="Javascript" implementation="..."/>

And if it works, how about the debug, I have an Intellij ultimate installed, but when I develop plugin with Community version, it always open a community version, so I should develop it in ultimate?

Thanks