Add simplified Chinese translation (zh_CN)

lang/languages.xml

@@ -29,5 +29,6 @@ List of available languages for your wallet's seed:
         <!-- <language display_name="Polski" locale="pl_PL" wallet_language="English" flag="/lang/flags/poland.png" qs="none"/> -->
         <!-- <language display_name="Português (BR)" locale="pt-br_BR" wallet_language="Portuguese" flag="/lang/flags/brazil.png" qs="none"/> -->
         <!-- <language display_name="русский язык" locale="ru_RU" wallet_language="Russian" flag="/lang/flags/russia.png" qs="none"/> -->
+        <language display_name="简体中文 (中国)" locale="zh_CN" wallet_language="English" flag="/lang/flags/china.png" qs="none"/>
         <language display_name="繁體中文 (台灣)" locale="zh_TW" wallet_language="English" flag="/lang/flags/taiwan.png" qs="none"/>
 </languages>

monero-wallet-gui.pro

@@ -291,7 +291,8 @@ TRANSLATIONS =  \ # English is default language, no explicit translation file
                 $$PWD/translations/monero-core_nl.ts \ # Dutch
                 $$PWD/translations/monero-core_pl.ts \ # Polish
                 $$PWD/translations/monero-core_ru.ts \ # Russian
-                $$PWD/translations/monero-core_zh.ts \ # Chinese (Traditional)
+                $$PWD/translations/monero-core_zh_CN.ts \ # Chinese (Simplified-China)
+                $$PWD/translations/monero-core_zh_TW.ts \ # Chinese (Traditional-Taiwan)
 
 CONFIG(release, debug|release) {
     DESTDIR = release/bin