Once you have an Original Caption Set for a project, you'll be able to create other caption sets for linguists to translate. To do that, choose "Bulk add caption sets" from the Project's dropdown menu on the project page, or click the blue "Bulk Add Caption Sets" button under the list of projects:
You'll be able to select which languages you wish to create a translated caption set for. You can use the "Select All" or "Select None" shortcuts to make it easier to choose caption sets.
To create a single caption set, click the blue "Add Caption Set" button under the list of caption sets on the Project Page. You can choose a language for the caption set, and it'll be created.