To install grace as a #lang language:
$ cd hopper
$ raco link grace
If you are using racket on a Mac, you may need to add raco to your path. In ~/.bashrc add a line:
export PATH=/Applications/Racket\ v5.3.2/bin:$PATH
(replacing 'v5.3.2' with whatever version of Racket you have)
Then do:
$ source ~/.bashrc