Which programming language would be best for me to learn?

HI All,
I work as product associate for contarct intelligence software company, Below mentioned are my skills, Can some one advise which language would be good for me to learn,
> I create usability documents
> Fair Idea about SQL
>Fair Idea about C
> Configuration management
> Creating impact and change request documents.
> Training clients on new releases

My product build is frame work would be ruby on rails and DB is Mysql.

Please Advise

Thanks,
Anil