Indeed it worked, thank you! Special encounter at council worked too, got the orders quest now.
Upd: Went to Fort Haledon, sucessfully finished the quest.
If anyone needs:
I've changed guard dialog in Scripts\t31Olgaidlg.txt like this:
begintalknode;
tag = 2;
state = -1;
nextstate = -1;
condition = 1;
text1 = "The vahnatai guards stands motionlessly at attention, alert for any threat that might invade and try to harm their leaders. When you try to speak with them, they ignore you.";
code =
set_spec_item(14,1);
break;
Just speak to Olgai guard and it will give you letters.
Edit: In these moments, I wish item editor was still present in the game.
Edit2: I've sucessfully finished the game, thank you Slartibus, you're saved my game progress, time, and nervs:)