Java has really good OTel coverage across tons of libraries. It should mostly Just Work™, though you'll still need to consider sampling strategies, what metrics you actually want to collect, etc.

Would say .NET isn't too far behind. Especially since there are built-in observability primitives and Microsoft is big on OTel. ASP.NET Core and other first party libraries already emit OTel compliant metrics and traces out of the box. Instrumenting an application is pretty straightforward.

I have less experience with the other languages. Can say there is plenty of opportunity to contribute upstream in a meaningful way. The OpenTelemetry SIGs are very welcoming and all the meetings are open.

Full disclosure: work at Grafana Labs on OpenTelemetry instrumentation