I believe the "Pulse" hero is bugged. I get the explosion sound, but no attack actually happens, it just runs around until it dies. That said, I don't have all the heros yet so I don't know if any others are bugged.
Some recommendations: An auto battle sort of mechanic would be nice, instead of being stopped by the pop-up upgrades. Perhaps a button to trigger the upgrades? Also if you could implement touchscreen compatibility, for those without mouse-and-keyboard.
Other than the language crossover (which I see you have addressed so no further comment), so far no noticeable bugs/immersion breaking! Great game, 8.5/10!