Seo on Multilanguage site...help me!!

hi, i have a client with a .it site.
But this site is multilanguage,
he has italian language on
mydomain.it
and he has 4 different subdomains
en.mydomain.it for english
fr.mydomain.it for france
de.mydomain.it for germany
ry.mydomain.it for russia


I need to rank 5 keywords for each language.
have i to work like 4 different site?
can i point backlinks, for example,
20 pbn on en.mydomain.it
20 pbn on fr.mydomain.it
etc??


what is the best way?
thanks

First of all you need to work on technical level seo on websites then you need go to do content based marketing for each website of each keywords.it does matter about count of links.which is close to your contents.all the best your wrk man