Use Reline.encoding_system_needs if exists

lib/irb/ext/save-history.rb

@@ -72,7 +72,7 @@ module IRB
       end
       history_file = IRB.rc_file("_history") unless history_file
       if File.exist?(history_file)
-        open(history_file) do |f|
+        open(history_file, "r:#{IRB.conf[:LC_MESSAGES].encoding}") do |f|
           f.each { |l|
             l = l.chomp
             if self.class == ReidlineInputMethod and history.last&.end_with?("\\")
@@ -107,7 +107,7 @@ module IRB
           raise
         end
 
-        open(history_file, 'w', 0600 ) do |f|
+        open(history_file, "w:#{IRB.conf[:LC_MESSAGES].encoding}", 0600) do |f|
           hist = history.map{ |l| l.split("\n").join("\\\n") }
           f.puts(hist[-num..-1] || hist)
         end

lib/irb/init.rb

@@ -296,14 +296,18 @@ module IRB # :nodoc:
   DefaultEncodings = Struct.new(:external, :internal)
   class << IRB
     private
-    def set_encoding(extern, intern = nil)
+    def set_encoding(extern, intern = nil, override: true)
       verbose, $VERBOSE = $VERBOSE, nil
       Encoding.default_external = extern unless extern.nil? || extern.empty?
       Encoding.default_internal = intern unless intern.nil? || intern.empty?
       [$stdin, $stdout, $stderr].each do |io|
         io.set_encoding(extern, intern)
       end
+      if override
+        @CONF[:LC_MESSAGES].instance_variable_set(:@override_encoding, extern)
+      else
         @CONF[:LC_MESSAGES].instance_variable_set(:@encoding, extern)
+      end
     ensure
       $VERBOSE = verbose
     end

lib/irb/input-method.rb

@@ -133,6 +133,9 @@ module IRB
       include Readline
       # Creates a new input method object using Readline
       def initialize
+        if Readline.respond_to?(:encoding_system_needs)
+          IRB.__send__(:set_encoding, Readline.encoding_system_needs.name, override: false)
+        end
         super
 
         @line_no = 0
@@ -207,6 +210,7 @@ module IRB
     include Reline
     # Creates a new input method object using Readline
     def initialize
+      IRB.__send__(:set_encoding, Reline.encoding_system_needs.name, override: false)
       super
 
       @line_no = 0

lib/irb/locale.rb

@@ -24,6 +24,7 @@ module IRB # :nodoc:
     @@loaded = []
 
     def initialize(locale = nil)
+      @override_encoding = nil
       @lang = @territory = @encoding_name = @modifier = nil
       @locale = locale || ENV["IRB_LANG"] || ENV["LC_MESSAGES"] || ENV["LC_ALL"] || ENV["LANG"] || "C"
       if m = LOCALE_NAME_RE.match(@locale)
@@ -40,12 +41,16 @@ module IRB # :nodoc:
       @encoding ||= (Encoding.find('locale') rescue Encoding::ASCII_8BIT)
     end
 
-    attr_reader :lang, :territory, :encoding, :modifier
+    attr_reader :lang, :territory, :modifier
+
+    def encoding
+      @override_encoding || @encoding
+    end
 
     def String(mes)
       mes = super(mes)
-      if @encoding
-        mes.encode(@encoding, undef: :replace)
+      if encoding
+        mes.encode(encoding, undef: :replace)
       else
         mes
       end