Standard displacement belongs to the treaty system

Would the Imperial Japanese Navy side with the Royal Navy on technical rules such as standard displacement?

The question may not arise in the same form because standard displacement was created by the Washington Naval Treaty; a different treaty would require its own definition and negotiation.

Standard displacement is a product of the Washington settlement. A world without that agreement would not automatically inherit the same definition. If a later treaty needed a common tonnage rule, Britain and Japan would have to negotiate it in that new context. Treaty language can therefore shape the technical vocabulary used to compare warships.