Add language settings for users, and translate titles to French

app/models/user.rb

@@ -5,6 +5,7 @@
 #  id              :integer          not null, primary key
 #  admin           :boolean          default(FALSE), not null
 #  email_address   :string           not null
+#  lang            :string           default("en")
 #  password_digest :string           not null
 #  username        :string
 #  created_at      :datetime         not null
@@ -22,4 +23,5 @@ class User < ApplicationRecord
   normalizes :email_address, with: ->(e) { e.strip.downcase }
 
   validates :username, presence: true, uniqueness: true
+  validates :lang, inclusion: { in: Languages::AVAILABLE_LANGUAGES.map { |lang| lang[:id] } }
 end