Add `LANGUAGE` env var to default pass list

[ulope]

Since tox 2.0.2 LANG is automatically passed to avoid Unicode(En|De)codeErrors. I've just now encountered a system (macOS) where LANGUAGE was used instead of LANG, again causing test breakage.

I would suggest to add LANGUAGE to the list of default pass variables.

[obestwalter]

Thanks for the report @ulope. Is that maybe a special configuration? I don't have a Mac here atm, but AFAIK mac uses the same LANG env vars like other UNIXES and Linux. Are there some official docs about this?

[ulope]

Yeah I hadn't seen it before either.
According to man 7 locale it applies to LC_MESSAGES.

It does affect Python's string handling however so I still think it would make sense to add it to the default "pass" list.

[pawelad]

Is anyone working on this feature?

[obestwalter]

Not that I know of. Go for it :)

[pawelad]

Should LANGUAGE be always allowed on both Unix and OS X or only on OS X?

[obestwalter]

AFAIK it's not used on Debian based systems. I'm on Arch Linux and there is also no LANGUAGE, so I would tend to say it's a Mac specific adjustment. It would be great if you could do some additional research about this before proposing an implementation.

[ulope]

It appears to be a standard feature: https://linux.die.net/man/7/locale (see section on LC_MESSAGES)

[pawelad]

It's not set on my OS X or my Ubuntu 16.04 but it is in the locale manual so I think it should be safe to add it.

[pawelad]

Pull request: #486