Some days ago both es_es and es_ar were deleted completely from both AMOS and downloads (see MDLSITE-2668).

It always was assumed that any user/course having such languages selected were not going to be affected because the older (now deleted) would exist forever in the dataroot/lang area and, in case of deletion from the UI, uses would be converted or default to the site lang.

But it seems that there are sites out there having any of them as default site language. And those sites are becoming sort of "locked" in the upgrade process with error:

Debug info: es_es

Error code: cannotfindcomponent

Stack trace:

    line 785 of /lib/componentlib.class.php: lang_installer_exception thrown

    line 640 of /lib/componentlib.class.php: call to lang_installer->install_language_pack()

    line 45 of /admin/tool/langimport/lib.php: call to lang_installer->run()

    line 1451 of /lib/upgradelib.php: call to tool_langimport_preupgrade_update()

    line 1527 of /lib/upgradelib.php: call to upgrade_language_pack()

    line 338 of /admin/index.php: call to upgrade_core()

At the same time, it's impossible (not easy) for them to go to the admin interface and change their default language, because the upgrade process is invoked continuously.

So, this is about:

1) Look for some workaround and inform about it in the forums.

2) stables: Provide some exception on upgrade for those (child) languages. Nasty, but it's the only way to allow the upgrade to continue, unless we decide to change it and allow to continue on error in general (don't think it's a good idea right now).

3) master only: Provide a proper upgrade step so any site/course/user use of the deleted langs is moved to "es". And it's documented in the release notes.