There. Is. No. Single. Factory.
The spare valves are made by a different company to the fuel injectors, which is different again to the training gear for the main armament, which is different to... you get the picture. To do this, you need pretty much the entire German naval industry to remain intact. It's a non-starter.
The Germans could be compelled to hand over the manufacturing drawings for every spare part on the ship, which in 1919 means an immense amount of paper. French factories would be perfectly capable of manufacturing them as limited-run parts, but because the design standards would be unfamiliar and quantities small, they'd be very expensive.
This is what was generally done in OTL when Power A needed to support Power B's ships. It could be done, but nobody liked it.