Four decisions, taken in order. Which markets justify their own pages at all. What URL structure carries them. How you tell search engines which page serves which market. And how far you go beyond translating the words.
The structure question is usually settled badly because it is taken early and quietly. Country domains signal locality most strongly and split your authority into separate sites, each earning links from scratch. Subfolders keep one domain's authority intact and are the right answer far more often than the industry admits. Subdomains sit awkwardly between the two.
Hreflang is where most implementations fail, and the failure mode is unforgiving. The annotations have to reciprocate: if your UK page claims the German page serves de-DE, the German page must point back. When they disagree, search engines do not pick a winner, they discard the set, and you are left with the duplicate-content problem the annotations existed to solve.
Then localisation, which is not translation. Currency, units, payment methods, addresses and phone formats, local trust signals, and the fact that buyers in different markets search using different words for the same thing. A literal translation of a page that ranks in English frequently targets a phrase nobody in the target market types.