So we should abandon aspirations towards human rights because Saudi Arabia or North Korea don't play along?
In the case of privacy from government seizure of private records the United States of America itself isn't even following its own Constitution and there is no reason to believe that other "Western" countries are either. So, why should anyone believe that anyone would follow an aspirational international treaty which undoubtedly would give for itself numerous ways to get around it?
Take for instance existing International Law agreed to in the "Universal Declaration of Human Rights":
No one shall be subjected to arbitrary interference with his privacy, family, home or correspondence, nor to attacks upon his honour and reputation. Everyone has the right to the protection of the law against such interference or attacks.
While I applaud the sentiment, I don't think any government thinks that it is being "arbitrary" when it conducts mass surveillance or wholesale spying. They say to themselves and their colleagues that they have very good reasons for doing what they do otherwise they wouldn't do it.
I would have no reason to think that any new treaty would be any more effective or have any fewer ways around it. Governments will always choose to carve out security exemptions at the very least which undermines the whole point.
The US Bill of Rights and the 4th amendment is(was) so special in that it isn't aspirational, but rather spells out the requirements and procedure for violating the right to privacy in fairly specific detail. And even then you see that it hasn't survived the test of time unbroken. I can't think of any other wording that would better survive even the best intentions of those tasked with our security.