Truces aren't properly displayed in enemy leader panels.

[Lessing]

I have a truce with Prince Alam of Egypt. Here you can see it in my county panel. (Truces aren't visible in the character panel, but that's another issue)



The proof in the declare war panel: yes, the truce exists. You can also see his other truces there (and ongoing wars), but not the truce with me.



Now Prince Alams county panel without our truce, but with all his other truces:



Looks like the truces between a character and myself aren't displayed on his panels.

edit: Ok, seems like the truce is unilateral, not bilateral. Quoting myself:

But then the question still remains how to see whether I have a truce with some enemy or not. As it is, it's pretty tedious... I have to either try to declare war on him (can't go that way if raised levies, aka cannot plan next move properly during current wars), or I have to click a county that I directly own.

 

[Chipster]

Truces only apply to the attacker. The defender in a war can turn around and declare war on you the day after you make peace, without any penalty

 

[Wezqu]

Truces are only for the aggressor of the war not for the defender. Defender can attack the aggressor immidiatly after peace if he so wants if he has valid CB's.

 

[Lessing]

Ah, that makes sense.

But then the question still remains how to see whether I have a truce with some enemy or not. As it is, it's pretty tedious... I have to either try to declare war on him (can't go that way if raised levies, aka cannot plan next move properly during current wars), or I have to click a county that I directly own.