This seems somewhat backward to me. It seems to me this data should be saved to a cache group that gets cleared on extension install/update and if we aren't already doing so there should be "critical" cache groups that are cleared on extension install/update.

right, first instinct was to solve the imediate problem and think later ?

anyway in this PR i do the same for the getContentLanguages (which, for now, is only used in associations edit), but those IMO we cannot cache to file (unless we clear the cache everytime we create/delete/change a content language).

so what do you propose, add a cache clean of com_languages everytime a language is installed/removed?
if so, i'm not very confortable with caching mecanisms and JInstaller, could you help pointing the way?

At https://github.com/joomla/joomla-cms/blob/staging/administrator/components/com_installer/models/languages.php#L257 add a call to JFactory::getCache()->clean('com_languages'); to the end of the method.

Edits to content languages already clear that cache group, see https://github.com/joomla/joomla-cms/blob/staging/administrator/components/com_languages/models/language.php#L262

So the part that isn't covered is clearing cache after a regular extension install or update. For install you could do something in https://github.com/joomla/joomla-cms/blob/staging/administrator/components/com_installer/models/install.php#L64 but you'd need to figure out what kind of data is available to you to only clear that cache for language packages/extensions. Funny enough, the controller method for that task clears the mod_menu cache always on success. The same applies to the update controller/model as well.

thanks a lot! will check that

i think (and hope) in the last comit i cover all installed languages cases.

content languages is another issue, because we need to clean the cache on every action ... even just changing the state of a content language in the list view. so, probably is better not to cache those...

ok @mbabker since the content languages is already been cached anyway i added it again.
See https://github.com/joomla/joomla-cms/blob/staging/libraries/joomla/language/helper.php#L134

please check if we can solve the installed languages cache the way i did it. thanks in advance.

This should work. I can't say that clearing this cache in the install adapters is a good technical solution, but I don't really have anything better for the moment so let's run with it so we don't lose the ability to cache this data.

I have tested this item ✅ successfully on ab7eca4

confirmed issue with cache
applied patch - no issue with cache

I have tested this item ✅ successfully on ab7eca4

I have tested this item ✅ successfully on ab7eca4

RTC