The PortableApps.com Launcher (used to create the AppNamePortable.exe launchers that handle app portability) uses .nsh translation files for localization. These nsh files are contained within the PortableApps.comLauncher\Other\Source\Languages directory when you have the PortableApps.com Launcher installed. They are also available for direct download.
Some strings are machine translated and should be reviewed. The English.nsh translation is the base from which other languages should be translated.