====== Webmail ======
Webmail in other language as in English:
open 
<code>
/var/www/ispcp/gui/tools/webmail/config/config.php 
</code>
and search 
<code>
$squirrelmail_default_language = 'en_US'; 
</code>
and replace in your lang abbreviations are in the file locale example for german  : 
<code>
$squirrelmail_default_language = 'de_DE';
</code>

====== Filemanager ======
Filemaneger in other language as in English:
open 
<code>
nano /var/www/ispcp/gui/tools/filemanager/settings.inc.php 
</code>
and search 
<code>
$net2ftp_settings["default_language"] 
</code>
and replace en in your lang. You find your language 
<code>
/var/www/ispcp/gui/tools/filemanager/languages
</code>
Example for german:
replace in 
<code>
nano /var/www/ispcp/gui/tools/filemanager/settings.inc.php
</code>
and change
<code>
$net2ftp_settings["default_language"] = "en";
</code>
in 
<code>
$net2ftp_settings["default_language"] = "de";
</code>
for German language