Comment by mrweasel

Java, .Net and maybe C/C++

For .Net at least SOAP support is built in, just standard .Net, no libraries required, just ask Visual Studio to load the WSDL and it will handle the rest.

I haven't used it myself, but a former colleague speaks fondly of gSOAP for integrating into C. When we've talked about it, his take is that using gSOAP would vastly reduce complexity and development time (compared to Java and REST), but this is an older gentleman who has been writing C since the 1980s.