`/api` allows for language awareness

[tomudding]

Through the LanguageAwareTreeRouteStack, all /api routes are language aware. This means that calling /nl/api/*, /en/api/*, and /api/* are all valid.

We have to figure out whether we actually want this or that we modify the route stack and associated listener to only allow en to be used without having to specify it in the URL. This would mean that only /api/* can be called and whathever it returns (that is not data) is in en.