Add translation: ja_JP

[ryuuta0217]

Good morning! (It is 5:00 a.m. in Japan)

I've added Japanese translation. / 日本語の翻訳を追加しました。 I'm Japanese, but my Japanese and English is poor.

[SpriteOvO]

Most of this looks fine, except that the locale is not added to CMakeLists.txt. Please add it and force-push your commit, then we can merge this PR :)

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -334,7 +334,7 @@ qt5_add_resources(APD_CODE_FILES "Source/Resource/Resource.qrc")
 #           https://stackoverflow.com/a/60848939
 #

-set(APD_TRANSLATION_LOCALES de_DE ko_KR zh_CN)
+set(APD_TRANSLATION_LOCALES de_DE ja_JP ko_KR zh_CN)
 set(APD_TS_DIR "${CMAKE_SOURCE_DIR}/Source/Resource/Translation/")
 set(APD_QM_DIR "${APD_BINARY_OUT_DIR}/translations/")

[ryuuta0217]

Ok! I'll try!