Can I use the AppleWatch4 in France? I have T-Mobile, and when I'm in France they use Orange, one of the European carriers that support the watch. But Apple says that the watch won't roam outside of your carrier's network coverage Explain please?

I have T-Mobile, and when I'm in France they use Orange, one of the European carriers that support the watch. But in footnote 2, Apple says that the watch won't roam outside of your carrier's network coverage. I'm confused. Can I use cellular roaming with T-Mobile in countries where their roaming partner works with the watch? I asked T-Mobile and they don't seem to know, other than to say that their network coverage, non-roaming, extends to Canada and Mexico.