I am trying to add support for a different language in Visual Studio 2010. I was hoping to add custom syntax highlighting, and have some sort of basic intellisense work with it.
It's not really for the faint of heart. Don't underestimate how much work you'll have to put in.
You'll need the Visual Studio 2010 SDK, and then to read (and re-read, and re-read(*)) all about Language Services
The purpose of a language service in Visual Studio is to provide language-specific support for editing source code in the integrated development environment (IDE). You implement a language service as part of a VSPackage.
(*) - unless it all immediately makes sense to you.
This isn't an answer on how to create custom syntax highlighting.
There is an open-source extension for visual studio 2010+ for Genero 4gl language support out of github:
https://github.com/gregfullman/VSGenero/wiki
It should do most of what you're looking for already, and it would certainly make a great starting point for you if you want to do more.