yes, they are not visible in mobiles devices, I found below article on the issue, I implemented a work around by including language names and flags, so when the secondary menu is active then at least the language name is visible.
On a separate note, I added the menu as a widget in the Header Right Sidebar, and it does not cover the full screen on a mobile, there is 20px padding on the left and right sides, how can I remove them only for the secondary menu so it can cover the full screen? Thanks, I appreciate your reply and great service !!
https://wordpress.org/support/topic/flag-from-language-changer-does-not-show-on-mobile-devices