Research the
EU Blue Card.
Different countries have slightly different requirements for the EU Blue Card. Here for instance are
Austria's. It is also not valid for the UK, Ireland and Denmark. But most of the rest of the EU will accept the EU Blue Card.
As regards language proficiency, with regards to work, don't be too worried. With the exception of France, you can get away with English anywhere. Indeed, in IT fields, as yours, English the predominant language of discourse.
There may however be requirements for you to learn the local languages to a basic (A1) level. I would say that your best bet is German as it would be accepted from the Netherlands & Belgium to Poland and down to Austria. If there is a Goethe Institut in your current city, sign up for a basic German course.