UI is with InDesign a question of the serial number. If the serial number support the required language you can install that language (if the installer contains the installer files for the language). For each language you have to make another installation.
Here on the Mac InDesign has not such menu item in preferences (as Photoshop has) to select a UI language for the next start. InDesign chooses the primery language from the Operating System. If you want to use InDesign always with a different language from your OS you must not install InDesign with the language of your OS.