Add option or default language=native (Opencage)

[terry90]

It's not uncommon to use the location's native language when geocoding (especially for forward geocoding).
Could we consider adding this as a default ? or would it be better to make it an optional parameter ?

[freyfogle]

As someone who lives in Barcelona I can tell you there are cases where it is highly contentious what the "native" language is.

In the case of OSM supplying "native" returns non-intuitive results. For example the "native" name for Belgium is a concatenation of all three languages of Belgium ie België / Belgique / Belgien Probably the only thing all three groups can agree on is that that is not correct ;-)

At OpenCage we take the approach of
a. obey whatever the user explicitly defined (which can also be language=native)
b. obey the browser language
c. default to English

https://opencagedata.com/api#language

[terry90]

Sure, but for now it's not even possible to chose the language when geocoding with this crate. I understand the case of non-intuitive native languages though.
I'll write a PR for this if this is OK. something to provide optional parameters, with defaults