On servers that have been upgraded many times, the languages on the WebClient login screen may be multiplied or wrongly displayed.
to solve it, delete all files in:
"c:\Program Files (x86)\Merak\" html\webmail\client\languages\
and replace with language pack from installer:
in total commander select IW installer and press ctrl + PgDn
and copy : setupwebclient.dat\html\webmail\client\languages\ to html\webmail\client\languages\
open IW installer (tar file) with mc and copy the same folder to same location