To export the en-US locale sources, make copies of the following directories and the files contained within:

Locale part Location on Linux Location on Windows
Controls used on ‘new-style’ Plesk pages, shared by Server Administration Panel and Customer Panel. /usr/local/psa/admin/application/default/resources/languages/en-US/ %plesk_dir%\admin\application\default\resources\languages\en-US
Locale of ‘old-style’ Plesk pages used in both Server Administration Panel and Customer Panel. Includes the file common_cli_messages_en-US.php with help messages for command line utilities It is highly recommended to not translate this file. /usr/local/psa/admin/plib/locales/en-US/ %plesk_dir%\admin\plib\locales\en-US\
Server Administration Panel locale. /usr/local/psa/admin/application/admin/resources/languages/en-US/ %plesk_dir%\admin\application\admin\resources\languages\en-US
Customer Panel locale. /usr/local/psa/admin/application/smb/resources/languages/en-US/ %plesk_dir%\admin\application\smb\resources\languages\en-US