Previous Versions URLs should preserve the language chosen

[Eric-Arellano]

We always will switch to an English version. That is annoying for other languages.

This would look like improving the logic in #267 to handle when locale/bn_BN is in the URL, e.g. https://qiskit.org/documentation/locale/bn_BN/index.html. The change should use test driven development by modifying our Jest tests.

[Eric-Arellano]

This should be much easier thanks to #321.

But, it is a little risky to add this feature because the locale may have not existed in prior versions of the docs. That would result in a 404.

[Eric-Arellano]

@coruscating had a great suggestion based on Python docs:

They will show an English page for an untranslated older version page.

We'd have to change our workflow to render all pages for different languages even if they're not translated though

[Eric-Arellano]

We don't version translations. https://qiskit.org/documentation/locale/fr_FR/stable/0.43/index.html and https://qiskit.org/documentation/stable/locale/fr_FR/0.43/index.html don't exist. So this is not even relevant.

It would be good to deploy translations for previous versions of the docs. But given that the docs are moving, this should be part of that new infrastructure rather than done via qiskit-sphinx-theme.