Thank you for your reply mate.
I have read the link that you gave me above. But my english is a little poor and the page seems a little confuse.
What should I do in my case?
My main domains
www.domain.com
French: fr.domain.com
Italian: itdomain.com
Russian: rudomain.com
Spanish: es.domain.com
What code should i put in the subdomains?
They have all the same content, but all text is translated.
EDIT: It seems that this is the solution for me:
https://support.google.com/webmasters/answer/189077
But where to add the code?
<link rel="alternate" hreflang="es" href="http://es.domain.com/" />
In main
www.domain.com ?
EDIT2:
I have added this code in my main
www.domain.com:
<link rel="alternate" hreflang="fr" href="http://fr.domain.com/" />
<link rel="alternate" hreflang="es" href="http://es.domain.com/" />
<link rel="alternate" hreflang="it" href="http://it.domain.com/" />
<link rel="alternate" hreflang="ru" href="http://ru.domain.com/" />
Should I put in all subdomains too?