I want to choose the way of language, change the selection method icon. How can I do?
The language selection menu is done with text. It can only be replaced by other text, by changing the language packs locally and changing the language name in them.
I don't see a possibility without diving in the code to put an icon there, but there is a forum discussion that might point some things out: https://moodle.org/mod/forum/discuss.php?d=200033.