Upgrade Weblate to latest 3.x
Weblate releases more often than we've been able to upgrade. Upgrading Weblate is a time consuming task because:
- Some minor versions can’t be skipped.
- There's (still) some manual work involved in managing dependencies.
- Problems may arise during Django migrations.
- Our own glue code may be affected by changes in Weblate Python API.
Despite that, it’s better do it earlier (or frequently) than accumulate.
This is the list of versions (as of today) that we need to migrate to, in order:
- 4.x (#17782 (closed))