It really depends on the language and what you want to do. There are tons of jobs in a variety of agencies. Some folks are interpreters, some teach others the language, some utilize the language in conducting analysis, and others just in their day to day operations overseas. A few agencies that utilize folks with language skills are the Defense Department, Department of State, The entire Intelligence community, DEA, DOJ....I honestly think that you can utilize languages in almost any agency that you are looking at, so then the question becomes what do you want to do with your language skills. I would suggest just looking at the Agency that you are interested in and see if you can some informational interviews with people who have those language skills.