Update environment variable that defines the language of the site, in "make backend-docker-start" command

[wesleybl]

The plone/plone-backend#170 PR changes the environment variable used to define the language of the portal when creating the Plone site with docker.

The make backend-docker-start command uses this variable. See:

volto/packages/volto/Makefile

Line 110 in 8521c5b

docker run -it --rm --name=backend -p 8080:8080 -v volto-backend-data:/data -e SITE=Plone -e ADDONS='$(KGS)' -e LANGUAGE='$(LANGUAGE)' $(DOCKER_IMAGE)

After the PR is merged and use in Volto of a release that contains it, the command should be updated.

Documentation must be updated as well.

[boss6825]

I have Updated Makefile and developing-core.md (documentation) to replace LANGUAGE with SITE_LANGUAGE
Is it enough or Should i make changes somewhere else also in documentation ?
will create a PULL request then ...

[boss6825]

I think i can't work on this issue as it has a new label of blocked ...

[stevepiercy]

@boss6825 you can work on it, but your PR wouldn't be merged until the PR on which it depends is merged.

[boss6825]

@stevepiercy then i will submit the PR today and will do the required changes in future if required accordingly