Incorrect aria-expanded on language button after language selection

[sculpt0r]

Type of report

Bug

Provide detailed reproduction steps (if any)

1. Open CKE4 with language plugin
2. Inspect the language toolbar button and find its aria-expanded attribute. At this moment it is set to false
3. Use the language button and select some language.

Expected result

What is the expected result of the above steps?

The aria-expanded attribute should be set to false since the submenu is folded. Also, screen readers shouldn't read this button at the current state as expanded.

Actual result

What is the actual result of the above steps?

The aria-expanded attribute is set to true. Screen readers read this button as expanded when any language is selected.

Other details

• Browser: -
• OS: -
• CKEditor version: 4.18.0 (reproducible even back to 4.13.0 - so no regression)
• Installed CKEditor plugins: language

[Comandeer]

The issue is not as simple as it looks and it's present on every menu button in the toolbar (e.g. "Text color"). It originates from the fact that menu buttons are in the "on" state in two situations:

1. the menu is open,
2. the content represents one of the menu options (e.g. the gray text would make the "Text Color" button switch into the "on" state).

At the moment we treat the "on" state as the indication of an open menu →

ckeditor4/plugins/button/plugin.js

Lines 347 to 350 in dabfeff

	} else if ( this.hasArrow ) {
	// Indicates that menu button is opened (#421).
	element.setAttribute( 'aria-expanded', state == CKEDITOR.TRISTATE_ON );
	}

We would need to come up with a better way to detect it.

[CKEditorBot]

Closed in #5255