To add additional localizable resources for sitefinity workflows refer to this blog post
on creating a custom resource class where the new types of content approval strings can be entered.
An exact three level of approval can`t be achieved as an option that sitefinity will fully support as all implementations follow the guideline that there are only two levels of approval workflow, however this doesn`t limit you on how many states of an item approval process you are going to add (Send for approval, Examine, Chekoout, Approval, Edit, Publish, etc.).
Add more branches to the workflow .xamlx file
containing new statuses for the items sent for approval.
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items