How to show the same program with two different language sets?

[Roberto <robicd gmx net>]

Hi guys,

 I'm trying to give my contribution to some italian translations. I 
need a way to start the same prog (the one I'm translating) both in 
english and in italian so that I can better understand where some terms 
appear and make a better translation.

I tried starting a terminal, then exporting LANG variable to en_US 
(tried en_GB too :-) and then starting 'yelp' (this is one of the 
program, whose .po I'm translating) but Yelp still runs in italian (my 
language default for the Gnome desktop I use).

The same procedure works with some other software (gqView, Xmms, The 
GIMP) and I can compare the appearance of every string both in english 
and in italian. Are Gnome applications (like Yelp) getting their 
language environment elsewehere?

What am I doing wrong? Any hint?

 greetings,
     Roberto