Yes and no. What I mean by that is it's possible to use CB Auto Actions with a Query action after the registration trigger to insert the user on all the other sites that way if they register on 1 it'll register them on all. However, this doesn't use proper APIs to create a user and is purely database based so you'll have to build and supply the queries for each site. Basically 1 query action per site on each site, so if you've 5 sites then each site should have 4 query actions for the other sites.

Maybe it would be easier to just make 1 website that is multi-lingual and have web addresses of the other sites point to the DNS of that 1 multi-lingual site, but then all of them would share all the same content, which I assume isn't exactly what you're wanting, but I believe it's possible to split content up using J2.5 and its language filter plugin which allows language specific menu links, modules, etc.. (e.g. a Spanish menu link won't display if viewing in English).

triggers works immediately or need the first login?

If using latest release then login and registration triggers will execute as if they were registering by normal means.

What about autologin? If user login at the mainsite how i can keep the same status for all slavesites?

It's purely session based so you'll need to after the login trigger create a session for the user in the database of the other sites. Then on logout trigger delete that session. You may need to use CB Query Field to pull a users session database table row params column so it can be inserted into the other database easily.