Section Translation surfaces the percentage of modifications the user makes to the initial automatic translation.
This information is included in different places: as feedback after editing a sentence (T259511), information of translated sentences (T260128), and publishing warnings when trying to publish (T260134).
This ticket focuses on creating an API that helps obtaining the necessary information to support the previous cases later.
There is a related proposal to improve how limits are calculated in Content Translation (T245840). It may make more sense to implement the new proposal rather than replicating the current one as it is (documented here). Other shortcomings of the current system (T251887) may also provide useful context for the implementation.