This certainly is not followed and I doubt the Pope pledged to it
He most certainly did. The Popes were virtually prisoner for those 59 years while negotiations were going on. That's what made things very tricky during WWII and why the prisoners had be very sneakily gotten out of Germany, so that the Church would not be seen violating the treaty. I have not gone into the later negotiations in depth, but I believe that with the evolving relationship between the Church and Italy, and with the jettisoning of Catholicism as state religion, the Vatican is for all means and purposes a fully independent nation with no strings attached in terms of international relations.
“I believe that with the evolving relationship between the Church and Italy, and with the jettisoning of Catholicism as state religion, the Vatican is for all means and purposes a fully independent nation with no strings attached in terms of international relations.”
The treaty seems to say otherwise though
I would agree and this explains that a Pope could speak out against Nazi Germany although it is was an alley of Italy
MIT BRENNENDER SORGE
On the Church and the German Reich
http://www.papalencyclicals.net/Pius11/P11BRENN.HTM