I've killed the leshen (3 times by different ways by reloading saves) and I don't get the "Woodland spirit" achievement.
I've followed the Sven way, so yes, I really killed it.

That's wrong ?

GOG Galaxy is still in beta. You have to wait for a fix.

Edit: By the way: You are not alone with this bug. Just search for "achievements" in this subforum and you will see it.

Search button doesn't work... But I suppose it's because galaxy is in beta...

I followed the trial in the quest the method told by the old man. After i returned stven tried to kill the elder man but i managed to save him there is a bug where if you go a certain distance away from dead stven he comes back to life to kill the elder man killed him 5 times have not checked if the elder man is still alive.

I've noticed this also. I completed that quest this morning completing the ritual and everytime I return to that village Sven reappears and attacks me... I've stopped to care, sincerely XD He doesn't attack the elder man, however.

I've experienced about 5 bugs where I did not get an achievement granted but did actually do the achievement. Well technically I didn't do the achievement I just played the game without thinking or caring and I accomplished the task that causes an achievement to unlock only without them actually unlocking but who am I to split hairs with the details. :)

Woodland Spirit is one of those quests that did not grant me an achievement. I've reported several similar ones to GOG via the GALAXY BETA thread for those who do actually care about achievements though.

In the end everything regarding Galaxy is beta and games using the achievements are probably going to have transient problems with them for a while.

With this specific quest another bug occurs though too and they might possibly be related. After I completed the quest (and it does how up under Completed Quests in the game), if I go back to the town, a certain person who met with a tragic end (whom I wont name to avoid a spoiler) is respawned in the town and attacks me on sight. If I kill him, he instantly respawns again and comes after me again. Also if you defend yourself against him the guards treat you as if you attacked an innocent person that was just minding their own business, even though it is a person who should be permanently dead, and so you basically can't kill him and you can't go to that town any more without 10 level 234234 guards chasing you around trying to kill you. Awesome bug.