You generaly loot from occupied territories, not from peer nations.
If Britain invades and occupies Egypt, and starts digging up artifacts that end up on a British museum, that's looting.
If some Frenchman digs up some artifacts in France, and then sells/trades/gives them to a British museum, that's not looting. Because the sale/trade/gift is not done at gunpoint.
In this case, if the artifact was not plundered from an (occupation of)/(war with Italy) to begin with, the most recent rightful owner is someone in Germany, not the nation of Italy.
Sure, that may be the case - but my point is that if French law allowed what I described, it wouldn't be looting, because France is a peer of the UK, as opposed to a vassal.
If Britain invades and occupies Egypt, and starts digging up artifacts that end up on a British museum, that's looting.
If some Frenchman digs up some artifacts in France, and then sells/trades/gives them to a British museum, that's not looting. Because the sale/trade/gift is not done at gunpoint.
In this case, if the artifact was not plundered from an (occupation of)/(war with Italy) to begin with, the most recent rightful owner is someone in Germany, not the nation of Italy.