My 2 cents: we are living in a certain time when where you live is not as relevant as what you do. IMHO, if you work in areas of high demand and few available professionals (such as machine learning, artificial intelligence, quantum computing, cybersecurity, machine-human interface, etc) you will be a desirable asset and will probably be in the position of choosing what offer is the best one for you. Recruiters are going crazy on Linkedin right now and before you ask they let you know that you can work remotely with very competitive salaries. So as an attempt to answer your question as of how to increase SWE salaries in Europe (as in any other place in the world really) is to consider making a move towards some hot career paths related to areas such as the ones I cited (not restricted to those obviously). I am a firm believer of this type of initiative. It might take time and be very challenging (and it will) but it definitely pays off.