It is also on zimbra wiki :
ZimletWritingTip
First, disable the deployed com_zimbra_ybabelfish.
When you deploy a zimlet, it is stored in the folder :
/opt/zimbra/mailboxd/webapps/service/zimlet/
-In this folder, create a folder "_dev".
-Inside _dev, create a folder "com_zimbra_ybabelfish"
-Put the files from com_zimbra_ybabelfish.zip inside this folder.
-Reload your browser.