A little background information:
In Keycloak 3.4.3.Final the following behaviour seems like a bug to me:
* Use a theme with a country-specific locale, for example fr-FR and a default locale
* Use Firefox on Ubuntu, drop all language preferences in its settings and just add
`french` (no country specified)
* request the login page
* the theme will be rendered in english
Acknowledging the RFC-4647 (1) Section 3.4; "Best Current Practice - Matching of
Language Tags - Types of Matching - Lookup" I would expect basic matching to be
applied so that the french language is chosen.
The topic is discussed cotroversely in the original Pull Request (2). Therefor I have been
asked to move a discussion from the Pull-Request to this mailing list.
For more Info, see also the related issue (3)
Thank you for your consideration.