Keep system language when changing settings

- when language was set to "system settings" and you changed any setting
  while BM was running, it switched the language to English.

src/bitmessageqt/__init__.py

@@ -2360,8 +2360,7 @@ def click_actionSettings(self):
 
             lang = str(self.settingsDialogInstance.ui.languageComboBox.itemData(self.settingsDialogInstance.ui.languageComboBox.currentIndex()).toString())
             shared.config.set('bitmessagesettings', 'userlocale', lang)
-            logger.debug("Setting locale to %s", lang)
-            change_translation(lang)
+            change_translation(l10n.getTranslationLanguage())
 
             if int(shared.config.get('bitmessagesettings', 'port')) != int(self.settingsDialogInstance.ui.lineEditTCPPort.text()):
                 if not shared.safeConfigGetBoolean('bitmessagesettings', 'dontconnect'):