Add the ability to set language parameter

[Kilatsat]

Similar to mapbox/mapbox-gl-directions/issues/129 we should be able to set the language code during initialization so that a French localized website can return French language directions.

[jojo12]

It's now more than a year since the previous post and nothing changed. It's a pity. I need it in german. how can I translate?

[DevIntact]

@Kilatsat @jojo12 : if you need it now, you can download and use this file https://github.com/DevIntact/mapbox-gl-directions-w-language

It is actually the same version of https://api.mapbox.com/mapbox-gl-js/plugins/mapbox-gl-directions/v4.0.0/mapbox-gl-directions.js but with the langage parameter which works

I don't know if someone will someday have a look on the pull requests dating since 2 years...