GnuCash language problem

GnuCash Portable running on a german system produces an ugly mix of german and english dialogs, help pages etc. I would like to tell the portable app to use english language only. In the non-portable version of GnuCash this can be done by adding the lines

set LANGUAGE=en_US
set LANG=en_US

before the command

start gnucash-bin %*

in the file gnucash.bat inside the bin folder (described here: http://wiki.gnucash.org/wiki/Translation).

Unfortunately this doesn't work for the portable version. Any suggestions?

Kind Regards

Tino