Considering the lack of an explicit close action, that will help to communicate that you can close the panel by clicking there again (in addition to click outside the list of languages) and avoid users to spend some seconds wondering how to close it.
(Copied as is from Pau's specifications.)
Version: master
Severity: enhancement
Yes. The idea is to keep the button as pressed (active state being of a darker grey) while the language selector panel is shown.
This is not a big blocker (since it does not prevent regular operation), but can help to better connect the button with the panel.
Change 284153 had a related patch set uploaded (by Santhosh):
Compact links: The trigger kept pressed while the panel is open
Change 284153 merged by jenkins-bot:
Compact links: The trigger kept pressed while the panel is open