Because the openid.realm is generated as
url('', array('absolute' => TRUE));
What this means is that the relying party will need to maintain multiple records for this site, since it will report different URLs based on which language page I was on.
My initial suggestion is to always use the default language to formulate the OpenID realm. This might however not be good for cases when domains play a part in language negotiation. Or better said, it is just a matter of perception. The same user on different domains showing the same site would probably equally be eligible to use his OpenID, so providing the default site root (without language affecting it) is the best as OpenID realm IMHO.