is it true that 3000-3500 PLN netto is already a great salary in Poland ?
No. 10,000 netto is great - 3000-3500PLN netto is actually below average in those cities.
if this is really the best you can expect when looking for a job as a freshly graduated engineer in Poland
It's as high as it's going to go for such a person. In your case, you're not going to get it - no Polish means no work.
Any hints about how much a foreigner telecom engineer (with an mgr.inż) and fluent in four languages could earn in the cities mentioned, would be nice !
In all honesty, the only language that matters is Polish.