The interface of a Bitdefender app is typically displayed in the language your Mac uses. By default, this is set to the language of the region where the Mac was purchased, but it can be changed to any of the languages that macOS supports. Changing your Mac’s system language automatically changes the language of installed Bitdefender applications.
Starting with macOS Catalina, you can change an app’s language without modifying your Mac’s system language. For example, you can use Bitdefender Antivirus for Mac in French and Bitdefender VPN in German while your Mac uses English as its system language. To do this, you can go to 
System Preferences, then click on Language & Region. From there, you can select the preferred language for each app. The Bitdefender app installed on your Mac will automatically use the selected language, if available.
Below is a step-by-step guide on changing the display language for any Bitdefender app on your Mac. Follow the instructions for your version of macOS:
Changing language for a Bitdefender app on macOS Catalina, Big Sur, Monterey
Changing language for a Bitdefender app on macOS Ventura
Repeat the above steps to change the language for any other Bitdefender app installed on your Mac such as Bitdefender VPN, Bitdefender Antivirus for Mac, Bitdefender Virus Scanner, Bitdefender Virus Scanner Plus, etc.