Fix the missing locale error

Merged: https://github.com/ruby/ruby/pull/6411

test/irb/test_history.rb

@@ -161,6 +161,7 @@ module TestIRB
     def test_history_concurrent_use_not_present
       backup_home = ENV["HOME"]
       backup_xdg_config_home = ENV.delete("XDG_CONFIG_HOME")
+      IRB.conf[:LC_MESSAGES] = IRB::Locale.new
       IRB.conf[:SAVE_HISTORY] = 1
       Dir.mktmpdir("test_irb_history_") do |tmpdir|
         ENV["HOME"] = tmpdir