Just bought the game, can't wait to play it :) However...
When I started the game for the first time, the language was set to German by default, most likely deriving it from the OS language settings. I'd prefer to play the game in English, though, so I tried setting the language to English, but this didn't work as expected: While "English" was selected in the language settings and the first entry in settings.json also read "LANGUAGE: en", all in-game text still was in German. Then I tried setting my OS language to English and this actually fixed the problem.
So setting the language to "English" currently sets it to "system default language" (or something like that). Hope this gets fixed in a future version :)