Steps to reproduce the issue

Try to load a frontend language file from a plugin running on backend. Error occurs when a backend language file already loaded. Language::getPaths returns something, because there's another file for the same extension.

Expected result

Nice translated text.

Actual result

Language constant.

System information (as much as possible)

Joomla 3.9.22, PHP 7.4

Additional comments

If I trying to use $this->loadLanguage('com_something', JPATH_SITE) in my plugin AND com_something's ADMIN language file is already loaded, CMSPlugin::loadLanguage skips loadig, because it doesn't check if $basePath matches or not.

CMSPlugin.php, from line 140:

		// If language already loaded, don't load it again.
		if ($lang->getPaths($extension))
		{
			return true;
		}