For translation use: http://www.poedit.org
and
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"

Send me the default.po and default.mo 

http://www.paehl.de

Test it before you send it.

Sample German:
Copy the default.mo and default.po in Arc_Convert\locale\de\LC_MESSAGES\DE
EN --> English
IT --> Italian
and so on. 
For more infos about your language see
http://www.poedit.org/translations.php

Restart the program and you can see ArcConvert in your Language