The language packs in Cinema 4D can be found under Help > Check for Updates and then by going to the 'Optional' tab.
If the machine is connected to the internet the 'MAXON Online Updater' should appear automatically when Cinema 4D is first installed and launched.
The following languages are included in all of the Cinema 4D packages:
Arabic
Chinese
Czech
French
German
Italian
Japanese
Korean
Polish
Spanish
If you need to add languages or would like to request a language not listed here it is advised to open a support ticket with Maxon directly as they will be able to provide either the correct files or look into adding your requested language.