I have tested this item ✅ successfully on db4e3bb

It indeed solves installing multilingual sampledata.

Note: The success response is not displayed (step8)

Thanks

Sorry to ask but Newbie here, when you fix something like that, how do I fix my actual test site. Reinstall ?, Update? Not sure How ?

You wait for the next release (Joomla 3.9.1 4.0 Alpha 6 in that case) or apply the PR using the Patchtester (https://docs.joomla.org/Component_Patchtester_for_Testers).

Thank’s Bakuai, I’m testing Joomla 4 alpha5-dev taken from —>
https://developer.joomla.org/nightly-builds.htm

And I add theCustom url —> https://update.joomla.org/core/nightlies/next_major_list.xml in my update options ?

4.0 is not for production yet at all. The upgrade option isn't guaranteed to work. So in this case, best bet would be to use the nightly builds and install fresh.

No, it don’t seem to work, I try to reinstall the nighty builds, It didn’t work ....
— I See Thank

Nightly builds are generated nightly. This PR was merged only 4 hours ago. So you need at least wait till tomorrow till it will show up in the ngihtly 😄

Nightlies are on a cron job to be built at 02:00 UTC daily. So they truly are "nightly" builds and not continuously regenerated each time a commit is pushed to one of the active development branches.

Thanks mbaker - Got it, I remark that the nighty build date is always today, I wasn’t so sure.
Great !

Thanks Bakuai — Installing Now!
Now I just need to understand how can I help more and how to use this forum.