The language code pairs used to generate the Installer file names are mapped in <sysdir>\X_Apps\X_Wix\Content\Languages.xml.
To support additional languages modify the Languages.xml file by adding an entry for the required language in the format:
<Language Id="WXYZ" Culture="wx-yz" Locale="2052" CodePage="950"/>
In addition, you will need to define an appropriate WIX localization file in …\X_Apps\X_Wix\Source, for example, file wx-yz.wxl.
When using Just In Time Upgrade, the languages.xml file must also be deployed onto the Application Server so that the correct MSI may be located. Without this file the English MSI will be searched for.