Pascal Birchler of the WordPress blogs some interesting research he did in the area of handling preferred language and how different systems – ranging from browsers, wikis, and social networks to all kinds of content management systems – approach and solve the problem.
Drupal 8 has a rather powerful user interface text language detection mechanism. There is a per session, per user and per browser option in the detection settings. However, users can only choose one language, so they cannot say (in core at least) that they want German primarily and Spanish if German is not available. But the language selected by the user is part of the larger fallback system, so it may fall back further down to other options.
The Language fallback module allows defining one fallback for a language, while the Language Hierarchy module provides a GUI to change the language fallback system. It allows setting up language hierarchies where translations of a site’s content, settings and interface can fall back to parent language translations, without ever falling back to English. This module might be the most interesting one for our research.
Apart from the research itself, I think this is an interesting example of how complex some seemingly simple features are.