Use the Locales screen to create a New Locale or to edit the settings for an existing Locale. The Locale record stores the locale relationships between the source language (shown as a parent locale in the screenshot) and translation language (shown as a child locale in the screenshot) settings used when you create a translation job. It also stores the translated variable values used during publishing for that locale.
You'll create the language pairs based on your translation needs, and then use the locale pairs when you are creating a Service Provider record. (When you create your service provider records, you'll assign one or more language pairs to the service provider's record. This will determine which service providers can be assigned to a translation job.)