docs: change update translation sessions in nox

[flpm]

What was done

Following the discussion in PR #397, this PR makes the following changes:

• Modify the update-translations session to only update translation files for languages in RELEASE_LANGUAGES.
• Added a new nox session update-langugage that can be used to update the translation files for a specific language.

This PR also fixes a small syntax issue in the documentation.po file for the Spanish translation (missing quote).

How to test

Run nox -s update-translations and confirm in the output that no languages are updated

❯ nox -s update-translations
nox > Running session update-translations
nox > Re-using existing virtual environment at .nox/update-translations.
nox > No release languages defined in RELEASE_LANGUAGES
nox > Session update-translations was successful.

Run nox -s update-language -- es and verify that the .po files for the Spanish translation are updated

❯ nox -s update-language -- es
(... some lines removed ...)
The message catalogs are in _build/gettext.
nox > Updating .po files for [es] translation
nox > sphinx-intl update -p _build/gettext -l es
Update: locales/es/LC_MESSAGES/tests.po +1, -1
Update: locales/es/LC_MESSAGES/documentation.po +1, -1
Update: locales/es/LC_MESSAGES/index.po +2, -2
Update: locales/es/LC_MESSAGES/tutorials.po +41, -19
Update: locales/es/LC_MESSAGES/TRANSLATING.po +2, -2
Update: locales/es/LC_MESSAGES/CONTRIBUTING.po +68, -15
Update: locales/es/LC_MESSAGES/package-structure-code.po +18, -18
nox > Session update-language was successful.

[sneakers-the-rat]

minor thing: i wonder if we can pick one term to refer to a translation or language? currently we have something like this

	update	build
single	`update_language`	`build_languages`
multi	`update_translations`	`build_translations`

i don't have a strong preference between four sessions vs two sessions s.t. with no arguments they build/update all languages but with an argument only update a single language (or only the released langs, etc), but i think in either case it would be good to pick either language or translation to refer to them

[flpm]

minor thing: i wonder if we can pick one term to refer to a translation or language?

Good point, that makes sense, maybe "languages" is more semantically correct?

[flpm]

I did a bit of reorganization of the nox sessions related to translations, to harmonize the names. I also simplified it a bit, to remove the internal build to release variable.

Here is the proposed setup:

• update-language: Update the PO files for a single language passed as a positional argument from the command line. E.g. nox -s update-language -- es. To be used by the language teams during early stages of the translation.
• update-all-languages: Update the PO files for all languages in LANGUAGES. To be used in dev, for tests.
• update-all-release-languages: Update the PO files for all languages in RELEASE_LANGUAGES. To be used in CI to keep PO files updated (see PR [ci] Ensure i18n up to date #397)
• build-language: Build the guide in a single language passed as a positional argument from the command line. E.g. nox -s build-language -- es. To be used in dev.
• build-all-languages: Build the guide for all languages in LANGUAGES. To be used in dev, for tests.
• build-all-release-languages: Build the guide for all languages in RELEASE_LANGUAGES. Called by the docs-test nox session, which is used in CI to build the guide for release.
• build-all-languages-test: A convenience function to run build-all-languages using the same parameters that docs-test used.

[sneakers-the-rat]

I like it - good with me :)

as an aside, since i'm not asking you to fix nox in this PR - the only thing i wish is that nox had a bit of a better way of sharing venvs, because each of these will make their own venv which makes things big and slow. making each of the sessions independent (rather than using notify) i think makes them tidier and easier to read than notify and posargs, which i like tho, so it's an improvement imo :)

[tkoyama010]

Thanks @flpm !

[sneakers-the-rat]

Wondering if we can merge this? i gave approval but i guess i don't have the right permissions or role or w/e to overcome the merge block.