Add Language model and LanguageController

spec/factories/part_of_speech.rb

@@ -1,6 +1,7 @@
 FactoryBot.define do
   factory :part_of_speech do
     sequence(:pos) { |n| "test-#{n.to_s}" }
+    language_id { FactoryBot.create(:language).id }
     definition { "test definition" }
   end
 end