Also change `navigator.languages`

[ygoe]

This extension sets the accept-language HTTP header but has no effect on JavaScript navigator.languages. That must be updated, too, or the effect will not be complete. For example the Mapbox GL API with the mapbox-gl-language plugin only considers navigator.languages but ignores the header so the map language cannot be changed with this extension. I have to change the browser language settings instead, which this extension aims to avoid.

Might be related to #14, they didn't provide any information about their problem.