In reply to Torsten.

@Torsten While I’ve felt the pain dealing with formal/informal translations, I don’t see that issue within the scope of a language-per-post feature at all. Formal/informal needs to be considered when installing language packs. Given the fact a switch between formal and informal within one and the same site would be an edge case at most (generally you’d pick one and stick with it for the whole site), I don’t see any case right now where bringing that switch to the level of authored content on a per-post basis would add relevant value to user experience in WordPress.