Not really anything to expand upon, I certainly support a universal pitch standard for modern western instruments, I just can’t find any reason as to why the Treaty of Versailles specifically included such a thing. I study late Renaissance and Early Baroque woodwind organology so I’m aware of the hilarious (to me anyways) history of tuning! I just want this one “why” question answered.
I am astonished to report that this is in fact true.
Treaty of Versailles Article 282:
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(22) Convention of November 16 and 19, 1885, regarding the establishment of a concert pitch.
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https://www.loc.gov/law/help/us-treaties/bevans/m-ust000002-0043.pdf
This is part of a list of 26 rather technical and fiddly treaties and conventions that the new Germany agrees to be part of.
I, too, would be delighted to hear more about it, but I wouldn't take it too seriously as a sign of widespread international concern over concert pitch.