I've solved it myself in the meantime, the reason for problems was so simpleand/or stupid that I also facepalmed.
Basically, I copied sod-dlc.zip to "dlc" directory instead of moving it, and (I think) the game was looking into it (the sod-dlc.zip file in the game's main directory) for dialogue lines, not finding Isra's there, obviously.
(looking over the Internet for help, I found some instructions like yours above, just stressing the need to move, and not copy, the zip file)
Removing the file from the game's main directory solved it.
Thanks for the help, anyhow.