If a new user registers then is directly added as a translator on the "Manage translators" admin page (admin/content/translation-management/manage-translator), they do not receive any email notifications when assigned a translation job. This is because the $user->icl_send flag has not been set. The flag is checked for on line 198 of icl_translate/icl_translate.notifications.inc before sending an email.

A temporary workaround is for the user or admin to edits and save their user account, setting the icl_send flag for the user account.

If it's supposed to default to "on" the icl_send flag should be set either on user registration, or when a translator is added on the "Manage translators" page.