I joined an alliance, Cerbu Bihor, in which the leader of the alliance and many other players have not been active for a very long time, my question, how could I claim the leadership of this alliance?
Short version: You cannot.
There is no function to “transfer” leadership from a “dead” or “inactive” leader.
Better off joining a more active alliance. Have a look in on #alliance-recruitment for some great options. Alternatively you can create your own “recruit me” thread in that same section of the forum.
Closing this topic before it desolves into a bunch of people trying to recruit out of the appropriate forum category.