VM_LANG -- how to create an instance of this class?

[Mister Paul]

Hi,

I need to create some translations for product types parameter.
I tried to use it by this code :
echo $VM_LANG->_('VM_MY_NEW_VALUE');
but it doesn't work : blank page...

Someone told me :

VM_LANG -- is a class, and you need to create an instance of class first, to use that method

But unfortunately I don't know how to do that...
What should I do ?

Thanks for your help !