Add Language model and LanguageController

app/models/definition.rb

@@ -1,3 +1,4 @@
 class Definition < ApplicationRecord
   belongs_to :word
+  belongs_to :language
 end

app/models/language.rb

@@ -0,0 +1,6 @@
+class Language < ApplicationRecord
+  has_many :definitions
+  has_many :part_of_speeches
+
+  validates_presence_of :name
+end

app/models/part_of_speech.rb

@@ -1,2 +1,3 @@
 class PartOfSpeech < ApplicationRecord
+  belongs_to :language
 end