No need for a gem for this one.
Simple Migration and Seeds file for adding Languages to your Rails app.
Run the migration or use the rails generator
rails g model Language name:string:index native:string family:string scope:string type_of:string iso_639_1:string iso_639_2b:string iso_639_3:integer:index
Scope: I = individual language, M = macrolanguage, S = special code
Type: A = ancient (extinct since ancient times), C = constructed, E = extinct (in recent times), H = historical (distinct from its modern form), L = living, S = special code
See Wikipedia for more information and source.
Copy over your seeds, seed them in your usual way, and viola!
That's it!