Thank you for interest to my theme. I have found solution of my task.
First of all the easiest way is to use a plugin, JSM-user-locale is good plugin for this task: wordpress.org/plugins/jsm-user-locale
Another way is to use standard WP functions.
You can get user locale with function
get_user_meta( $user_id, 'locale', $single = true );
Site localization ...