MOSCOW, Aug. 28 -- The word Moscow keeps reaching for is the one word that guarantees it loses.

Artem Studennikov, who runs the First European Department at the Russian Foreign Ministry, told RIA Novosti this week that France's repeated boarding and diversion of tankers carrying Russian crude amounts to piracy and robbery at sea. It is the same formulation the Kremlin spokesman Dmitry Peskov used in June, when he said French actions "border on international piracy," and the same one the Russian embassy in Paris used after the most recent seizure. The phrase is vivid. It is also, under the treaty Russia signed and ratified, unavailable.

That distinction is not lawyerly bookkeeping. Somewhere inside this dispute Moscow has a genuine legal...