In the last project, we had an unusual requirement, create a system of translations that can inherit from parent translation (language), it's how Language Hierarchy (https://www.drupal.org/project/language_hierarchy) module was born.
Let's imagine following scenario:
We have a website with three languages, English, Spanish (es) and Spanish from Mexico (es-mx).
Content editor translate website to Spanish (es), but only a few pages would be different from Spanish in Mexico (es-mx), it's where Language Hierarchy module could become handy. It can help to inherit translation from parent language that, in this case, would be Spanish (es).
It's also possible to create multiple levels of language hierarchies:
In this session, I will talk about module's construction and what challenges we encountered.