Localization project owners and project administrators can add a contributor (translator) to specific languages in two ways, as described below.
In the Project Page
Go to your project's main page, and you will see next to the translation progress of each language, on the right, three Action buttons. To assign a contributor to a language, click on the first button in the row, Add contributor.
In the Language Page
Click on any of the languages in the project page, and you will be taken to the language page, where contributors do the actual translation work. In each of these pages, you will find a side menu. Here, you can assign contributors by pressing on the button called Add Contributor.
How contributors are notified about being added to a language
If the translator doesn't have a POEditor account, they will receive an email to let them know you added them. The account will be created automatically, the translator will only need to activate it by clicking on the activation link in the email.
If the translator does have a POEditor account, they will receive an email informing them that you added them, with a link to go directly to the translation page.