It looks like I SOLVED the problem.
Even though it doesn’t make much sense to me I fixed it doing as follows:
go to SETTINGS->languages->settings and choose again settings under “URL modifications”.
Choose “Keep/language/ in pretty permalinks” (mine was previously set on “Remove/language/ in pretty permalinks” and the link to the home page in english didn’t work). I tried to switch back to “Remove/language/ in pretty permalinks” and it didn’t work once again so this must be the culprit.
Somehow the permalink this way tricks the plugin, even though the difference should be only in the way the link is displayed…or not?!