To complete the sitemap with the translations indirectly related by language we uses the hook links alter to process this
To improve the performance, this part can be moved into the Url generator.
Change language hierarchy filter to hook links alter, to a entity Url generation, using the option of skip untranslated to bring the direct translations and a logic to bring the translation by hierarchy.
This change depends of the Language hierarchy cache solution
Closed: won't fix
1.0
Code
It affects performance. It is often combined with the Needs profiling tag.
The module was refactored on 2.0.x, moving this to closed.