Thank you! Okay, I must have made a mistake in the English version of the game that's causing a bug when entering that quest log. I thought I had already fixed it, but apparently not. I'll make sure to fix it properly once and for all this time.
In the meantime, please avoid opening the quest log for that particular quest, and you shouldn't run into any problems. If you need help with your current quest, feel free to ask me instead.
Sorry once again!