Stake customer support thought I was asking the "language" of the casino as in English and all that, bitkong didn't replied yet at all. I think the safest option to assume could be c# for now, at least for the gaming parts of course because that would be the easiest option yet again to build these games on C# but I am not entirely sure how the payment part of it is coded since it could be anything.
The thing is that C# is very versatile, and it's incredible, but the programming part is very extensive, and judging by the number of jobs that there are for programming casinos and that I've seen on the web many programmers ask for C# and Java, and that's not just because they are the most common languages, but partly because they are easier for a programmer, there is much more that can be programmed, but I think that C# and Java are the most standard, and I agree To this, any programmer will be able to quickly understand what another did in case he no longer works with the company in question, and since Java also has so many scripts, it is also adaptable. In fact, I have looked for some jobs as a programmer engineer and what they ask for the most, at least in Spain, is that they can do it in C or Java.