patch 8.2.4420: menu translations are inconsistent

Problem:    Menu translations are inconsistent.
Solution:   Add a Makefile to convert between encodings. (Ada (Haowen) Yu,
            closes #9801)
diff --git a/runtime/lang/menu_ja_jp.utf-8.vim b/runtime/lang/menu_ja_jp.utf-8.vim
index 5835868..1f3c429 100644
--- a/runtime/lang/menu_ja_jp.utf-8.vim
+++ b/runtime/lang/menu_ja_jp.utf-8.vim
@@ -3,6 +3,7 @@
 " Menu Translations:	Japanese (UTF-8)
 " Last Translator:	MURAOKA Taro  <koron.kaoriya@gmail.com>
 " Last Change:		18-Jul-2018.
+" Original translations
 "
 " Copyright (C) 2001-2018 MURAOKA Taro <koron.kaoriya@gmail.com>,
 "			  vim-jp <http://vim-jp.org/>