Add Language model and LanguageController

spec/factories/definitions.rb

@@ -2,6 +2,7 @@ FactoryBot.define do
   factory :definition do
     pos { "n" }
     definition { "this is a definition" }
+    language_id { FactoryBot.create(:language).id }
     word_id { FactoryBot.create(:word).id }
   end
 end