Default translators vs. Preferred translators
Default translators are linked to a particular client and language pair. You can define one or more to each row in the price list in each client's profile.
Default translators are then offered in sub-projects with that client with the given language pair. To open the list of default translators for selection into the current sub-project click on the 'Default translators' button in the sub-project screen.
Preferred translators, by contrast, are linked to language pairs in general, independent of clients.
In the sub-project screen there is a filter (checkbox) to optionally filter the translators in the dropdown list accordingly. In Program settings / Project Management there is an option to activate this filter by default in each new sub-project.
To assign a translator the 'preferred translator' status for a particular language pair tick the checkbox in this translator's price list.