I have printed international stamps for the UK before without problem but had endless problems this morning trying to do the same. Try as I might I couldn’t find an international option unless I used the “professionals” page - where the tariff is €1.30 for up to 20g. However, without being registered as a business you can’t complete the purchase.
Then I had a thought, as I had been using Google Translate to make the page easier to navigate and when I turned this off and started again then lo and behold the international option appeared. The rate is indeed €1.47 for up to 20g and I printed a raft of stamps for Christmas with no problem.
Then I started again, planning to print some more with a different picture, but this time (still in French) although I clicked the button for international, the destination drop-down menu only had France or overseas territories listed, with the lower tariff showing. Repeatedly re-trying eventually got it to work.
Just thought I would mention this in case someone else had the same problem - it can be done! 