In most cases Vegas Pro users will know which localisation they'd need before installing. Else one could either re-install or use SeMW extension. Not a big deal.
Install the language you want from the beginning: link (Deutsch, English (US), Español, Français, Português (Brasil)) are the choices.
Since Keys are locked to particular regions, this will not work. When you try to register Vegas Pro 22 in a language that is not the original purchased one, it will fail with code -14.
It's insane and doesn't make any sense. It would be one thing to require reinstallation of software to change the UI language, but to actually region lock it is just incomprehensible.