You should have received an e-mail to join Discourse and you are ready to find all the relevant information before you start to experience Proton Localization.
Click on the link that you received for the invitation to Discourse.
Then, fill in the required information. One thing to mention: use the same username as your Crowdin account.
After you click Accept Invitation, Proton will receive your application to join and you will see this screen.
After your profile is validated, you can access all relevant information to ramp up your localization experience! Let us know if you come across any issues during the sign up process by reaching out to @PMtranslator.