Fine by me - it looks like a bug as it is correct in the .sys.ini file and thats the file used for the dropdown menus

Although both .ini and sys.ini do load, the string is picked from the .ini in multilingual associations (nothing to do with menus dropdown)
Same for all these types.

yes i was just pointing out that the menu dropdowns are all correctly plural

I have tested this item ✅ successfully on 2b339a2

BTW, I found why .ini superseeds sys.ini in multilingual associations.
In the helper, we have in the getSupportedExtension method

		// Get the translated titles.
		$languagePath = JPATH_ADMINISTRATOR . '/components/' . $extensionName;
		$lang         = JFactory::getLanguage();

		$lang->load($extensionName . '.sys', JPATH_ADMINISTRATOR);
		$lang->load($extensionName . '.sys', $languagePath);
		$lang->load($extensionName, JPATH_ADMINISTRATOR);
		$lang->load($extensionName, $languagePath);

		$result->def('title', JText::_(strtoupper($extensionName)));

and further

if ($lang->hasKey(strtoupper($extensionName . '_' . $title . 'S')))
			{
				$languageKey = strtoupper($extensionName . '_' . $title . 'S');
			}

Mystery solved. ;)

just wondering if that needs to be fixed as perhaps it will cause issues with non core extensions using associations?

I think we must have had a reason for that.
One of the requirements for 3rd party extensions (among a lot of others) is to provide such string in the .ini, if not already present.

I have tested this item ✅ successfully on 2b339a2

RTC. Thanks for testing.