Hi Vlada,
for now I use the Zope 2.7.5 tarball. I write freelance (not bound in a product) page template and wish it to be i18n'ed. I have appropriate tags inside and the domain set at the top. There is also Plone with its products in that instance.
Where should I put the PO files, so the messages can be substituted? Normally you have to put them inside a i18n folder located in your product tree. However, according to your message, you don't have a python product, so, I guess, you have to look for the plone's i18n folder and put your PO files there. The only problem I see here is that you have to remmember it every time you update plone.
I'm not sure if this would work: you could try to create a dummy folder, let's say MyTranslations, inside the Products folder of your instance. Then create an empty __init__.py file and add a 18n folder to put your PO files. Regards, Josef