[reaperducer]

There isn't a rule about that sort of thing, but a convention you get used to over time.

Adding the Les gives Olympiades more context. The extra word provides clues that this is a straight foreign word that should be treated differently. Port d'Italie is already two words, so extra context isn't necessarily needed.

Like many things in English, it's up to the speaker/writer, and the context.