[fix] add listbox role to lang selection dropdown listbox and make its items behave like options

Currently when we use tab on the navigation bar, the navigation goes over language options one by one. To avoid that I have added a tabindex=-1 on the link inside li items. This way when we use tab, we stop on the language selection widget only once, and can navigate among options only with up and down keys.

I have also added listbox and option roles to the language dropdown to indicate that it's a listbox where a choice can be made.