mnlg:

qwertz:the tts voice also add a "half german j to the end of some consonant". Don't ask me excactly what it is about

Stab in the dark here, but it might be that there is a palatalization in progress. From the page I just linked:

"indicated by a superscript 'j', as [tʲ] for a palatalized [t]"

Seems to be that this is something typical to the polish language. That polish people adds half german "j"/english "y"(?)... to the end of some consonant.

An "half J/Y" means that you can hear slightly a "J/Y" after i.e. "Jacek" So the polish pronouncation for "Jacek" sounds like "JacekY" (the english way) or "JacekJ" (the german way). It's not a hard cutted "k" consonant like i.e. in german.

So, the regarding polish-text-to-speech software adds this, too. Just try it yourself at the ivona (Jacek voice) website. Sorry, I don't know the english linguistic term for that. In german it is "moullieren".

Btw. I also heard that asian people have some problems to pronounce two following consonants i.e. "nk" inside "dankon". Could be a small construction weakness of the esperanto language building.