Describe what maintenance you would like added.

The I18N step in our docbuild on often takes longer than two hours to complete when run on main:

This means it can take around 3 hours from merging a PR to being able to merge another unless we decide to ignore the doctest, in which case our CI on main has failed documentation runs due to concurrency.

As far as I know I18N doesn't support multi-process building nor respects the number of sphinx jobs and I'm unsure what workaround to propose except to disable unless on release or simply wait the three hours for the CI.

Links to source code.

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