Automate i18n POT file updates in PRs

[webknjaz]

          > It'd be a good idea to have automation that would do this on its own. A-la pre-commit.ci. Would you be open to exploring this? I'm pretty confident I know how to implement it.

This is an interesting idea, and I'd very much be open to learning more about this! One of the challenges is how to manage merge conflicts on this kind of thing, so I'm curious how you might approach that as well. #6631 has some background on translation workflow ideas

Originally posted by @miketheman in #17602 (comment)

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@miketheman yeah, I was around back then but forgot about that thread :)

FWIW, my current idea was to do the same as the status quo but automatically. It doesn't handle merge conflicts. When a PR has conflicts, the CI doesn't run and usually no integrations run either.

Though it's worth noting that I've since implemented a somewhat different workflow over @ PyPUG — we have no POT file, nor do we have POs/MOs in the default branch. But there's a separate branch translation/source which does. Whenever a PR is merged into the main branch, the CI merges main into translation/source. And this is how the POT file remains up-to-date. Weblate is configured to work with translation/source too — it sources POT from it and sends PR with translated files against this branch as well.
So both POT and POs end up in translation/source. The process is unidirectional and there are no flows that would attempt updating the same files. translation/source is also never merged back into main.
So main only holds the original English version. It's the source of truth.
And RTD is set up to build from translation/source and not main too.

graph LR

  subgraph "🌵 'pypa/packaging.python.org'"
    branch:translations["🌿 'translation/source'"]
    branch:main["🌿 'main'"]

    persona:writer("🧔 Writer (produces English text)")
  end

  subgraph "🗂️ Weblate"
    persona:translator("🧔 Translator (produces non-English text)")

    strings:src["📝 Source strings (English)"]
    strings:translated["📝 Translated strings (non-English)"]
  end

  subgraph "📝 ReadTheDocs"
    rtd:br-pt["🇧🇷 Brazillian Portuguese docs"]
    rtd:en["🏴󠁧󠁢󠁥󠁮󠁧󠁿 English docs"]
    rtd:uk["🇺🇦 Ukrainian docs"]
  end

%% Contribution directions:
   persona:writer --1--> branch:main

   branch:main --2: POT file is generated--> branch:translations

   branch:translations --3--> strings:src

   strings:src --4--> persona:translator
   persona:translator --5--> strings:translated
   strings:translated --6: Weblate sends a PR with PO file updates--> branch:translations

   branch:translations --7--> rtd:br-pt
   branch:translations --7--> rtd:en
   branch:translations --7--> rtd:uk

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