Back when I was working on GOV.UK Verify we had URLs that looked something like /verify-passport for English and /cy/verify-passport for Welsh. I made the decision that if readable URLs was a design goal they should be readable in both languages, and ended up localising them all to (for example) /verify-passport and /gwirio-pasbort. No idea if anyone ever noticed, but sometimes it’s nice to sweat the small stuff.
What do you do when the translated slug happens to be the same in multiple languages? I ended up still having the country code in the slug.