@MarcoAurelio has said a full scap & l10n update is needed. I checked wikiversions.json last night and see 4 impacted wikis to run namespaceDupes.php on.

Why are we backporting namespace changes anyway? Can they just not ride the train?

In T253070#6148490, @Reedy wrote:

Why are we backporting namespace changes anyway? Can they just not ride the train?

They require namespaceDupes.php to be ran so it was decided this was the safest way.

In T253070#6148491, @RhinosF1 wrote:

In T253070#6148490, @Reedy wrote:

Why are we backporting namespace changes anyway? Can they just not ride the train?

They require namespaceDupes.php to be ran so it was decided this was the safest way.

Well, yes and no. namespaceDupes.php is required if people have created pages using those namespaces before they actually existed. If they didn't, it's not needed (or will be a no-op).

Lots of wikis probably need it running.

There's also no reason it can't be run after the train runs. I'd suspect the number of affected pages is going to be minimal

There's also no reason it can't be run after the train runs. I'd suspect the number of affected pages is going to be minimal

It could be. We chose this method as well as it also avoids it being impacted by a train rollback and will ensure that it remains done now.

Overall, it’s slightly safer, ensures the script is ran straight away, ensures they remain translated once deployed even if a rollback happened.

In T253070#6148573, @RhinosF1 wrote:

Overall, it’s slightly safer, ensures the script is ran straight away, ensures they remain translated once deployed even if a rollback happened.

It doesn't matter. We don't store the NS prefix in the database if the NS is in MW (only when it doesn't exist, the page goes into NS0 with a title of NS:Page). So if the user NS was renamed, a page created, then that NS goes away, the page will still be viewable at the old NS for user.

Sure it breaks any links using the explicit text, but those will be minimal, as I doubt they'd start linking using the NS automatically.

And namespaceDupes would be only needed if a page was manually created at NewNW:PageName in the short time (unlikely I would suspect)

Massive thanks to @Catrope for ensuring I didn't go insane. A seamless 2 hours!