Note: I also think the language load can be simplified
from

$language = Factory::getLanguage();
				$language->load('com_menus', JPATH_ADMINISTRATOR, 'en-GB');
				$language->load('com_menus', JPATH_ADMINISTRATOR, $language->getDefault());
				$language->load('com_menus', JPATH_ADMINISTRATOR);

to simply

				// Load the language files
				$language = Factory::getLanguage();
				$language->load('com_menus', JPATH_ADMINISTRATOR, null, false, true);

test this Weekend now.

After save new Article no Button "New Menu Item" is shown.

System information

• Nightly Build 4.0.0-alpha5-dev
• Multilingual Sample Data (French, German DE, Persian)
• Template: Cassiopeia
• macOS Sierra, 10.13.6
• Firefox 61 (64-bit)

CloudAccess.net

• PHP 7.1.15
• MySQLi 5.7.18-cll-lve

hmm. The new button stuff was created in #21357 2 days ago.

#21357 is merged so the Button should show. Installed Nightly 2 Times, get as always the "AJAX-Error" at end of Update but not the Button.

I have tested this item ✅ successfully on 9d562e5

Works as expected after new Installation of Nightly (not Update as before).

@infograf768 did not thougt about this, thank you
@franz-wohlkoenig many thanks for testing again

@bene-we thanks for your Work.

@bene-we
Please set your test OK in https://issues.joomla.org/tracker/joomla-cms/21391 by using the blue button "Test this"

Note: will create the new PR for lang load separately.

I have tested this item ✅ successfully on 9d562e5

Ready to Commit after two successful tests.

Thanks JM!