AO3-6868 Add rake task to check for duplicate language names

lib/tasks/language_tasks.rake

@@ -0,0 +1,19 @@
+namespace :db do
+  desc "Check for duplicate language names before adding unique index migration"
+  task check_language_name_duplicates: :environment do
+    duplicates = Language.group(:name)
+      .having("COUNT(*) > 1")
+      .count
+
+    if duplicates.any?
+      puts "Duplicate language names found:"
+      duplicates.each do |name, count|
+        puts "#{name} appears #{count} times"
+      end
+
+      abort("Please resolve duplicate language names before running migrations.")
+    else
+      puts "No duplicate language names found."
+    end
+  end
+end