They were never a thing in Europe.
Not really a thing in Canada either. Bought a reasonably midrange ($600k) brand-new apartment back in 2006, it didn’t come with it. Also have never seen it in any other house that I’ve visited, except for the wealthy. And by that, I mean in a house that you would normally pay $4-8 million for. Which is certainly upper middle class where I am, but not overly wealthy.
C# has had string interpolation for, what - nearly a decade, now? It arrived with C# v6, which was released in 2015.
Meanwhile Java just pulled their implementation out of the latest beta earlier this year because they couldn’t get it to work right.
Don’t know about you, but I think that Java is largely resting on its laurels as of late. That the only real reason to go for it is it’s third-party library system, and not much more.