There's other things like GDPR, local taxation, many cross border laws, and by culture I mean a variety of things: you'll see university graduates flogging themselves to death in Silicon Valley, but a start up in London will be slightly more relaxed by comparison. In the US, "free VC money" means there's an incentive to get to market asap, monetize, and move on. That doesn't really exist in Europe.

Where i18n becomes nasty is when you have to find, evaluate and constantly coordinate with n external translation agencies. Working from Germany on an international product, this is a nightmare. From a technical standpoint we can release features within a minute thanks to our CI/CD setup, but as soon as some user-facing text is affected we have to hold changed back until all translations were collected.