Override language prefix per domain

Problem/Motivation

Currently it is not possible to override the language prefix per domain.

For example on domain X we want Dutch to be /nl, on domain Y we want it to be /nl-nl, and on domain Z we want it to be /.

Proposed resolution

Read the custom suffixes from domain.language.{domain}.language.negotiation.

For example:

domain X

languages:
  nl-nl: /nl

domain Y

languages:
  nl-nl: /nl/nl

domain Z

languages:
  nl-nl: ''