I can not see a certain language in the Interface language dropdown menu on the PCC login screen.
According to the OBAS Provider's Guide:
Available Languages Check the boxes next to language names to allow your customers to switch the interface into these languages. The list of languages in this section is comprised of the languages shipped within separate language packs with Odin Business Automation Standard kit and installed during the Odin Business Automation system configuration.
Top > Configuration Director > Miscellaneous Settings > Regional Settings, press Edit and enable the language(s) required.