Hi Joachim,
thanks a lot for the Polish translation! I will include it in the next release.
As for your GPX file: That is really strange. My plugin opens and parses the GPX file, and that part works fine - it shows the track length, number of track points etc., so that's not the problem.
For some reason the Openlayers API seems to have problems with the track, though, and i really can't say why...
I'll try to analyse what's wrong, and will let you know if i find out.
cheers,
Frank