I don't think they're working at all, actually. They don't get adjacency either.

Quoting 00zim00,

reply 2

Could maybe a Dev chime in please, seems most people are confused. Unless a person who knows how to mod can check in the game files or something hate to think they are just broken..

Agreed.  I was going to post the same question before I saw the OP's one.  I had a game were I built embassy's on most of my planets but did not see any difference in the diplomacy screen.  

Devs arw embassy's broken? 

Can someone ask this in a dev stream if the devs dont reply here, the cast is at 5am for me so I am rarely able to make it

I must just chime in that it seems like +1 diplo every time you build a building seems insanely powerful to me.  No idea on whether it's working as described, but building 10 buildings and getting +10 diplomacy seems really broken. 

Just saying...

I'm pretty sure they work exactly like what some here have suggested, namely that they each provide +1 Diplomacy. I think the reason you aren't seeing the benefits on the Diplomacy screen is that the Positive/Negative modifiers (+++ / ---) are visually capped at 3, but their benefits can go beyond that. The basis I'm using is a game where I have had enemies being hostile towards me for quite a while, but after I built quite a few of the Buildings, everyone was suddenly "Close" relations with me. This is in contrast to the actual +/- diplomatic situation I currently have with several of the factions. Based on my experience, they shouldn't be "Close" to me with the modifiers in place (I'm definitely not having a higher Mility rating than them either).

This leads to a game where the computer has no incentive to attack me, opening up for any potential Victory condition I want. Pretty unbalanced in my opinion. (This isn't in 1.5, I don't know if that fixed it).

That response got me thinking. I read somewhere about the different "Personalities" of the AI, that some of them value diplomatic relations higher than normal and some of them value them lower than normal. Perhaps the Malevolent ones in your game are Xenophobic (All diplomatic pluses are halved, and all diplomatic minuses are doubled), which would explain why there is such a discrepancy. Source: http://galciv3.gamepedia.com/Personality

I did end up asking Paul not long after this post on the Galciv3 dev stream. I had a quick look on the utube page for the exact video but couldn't find it.

BUT from memory all Diplomatic Bonus does (from the embassy) is help prevent further degradation of a races opinion of you. If they already hate you it wont help much if at all, if they like you it will be harder for them to hate you. So in a way its more about keeping all races at there current opinion levels and not so much about increasing it. Likewise they are only useful early on before other races start getting to many negative modifies towards you as it dosnt boost there opinion as it only keeps it stable.

So unless your focusing on building them VERY early game they are kinda useless. And in fact mid to late game there are totally useless in my opinion :/.

That is, if it hasn't changed in some patch between may and now.

Just a side note, to confirm the Diplomatic Bonus does not gives a + bonus to you or a race as i originally questioned in my first post. Despite there similar name they arnt directly related.

Strangely enough, the Techs and some unique 1 off buildings that give a +1 Diplomatic Bonus do in fact Give the +1 bonus to relations as you would expect to races. So they do make races like you more and counteract the negative modifies. Its only the Embassy itself that acts differently, which i presume is because you can build so many. I have no idea why they have the same/similar Bonus name even know they are different, its all rather confusing :/.

But they are both different, and to answer your question there is no way of knowing what exactly your total embassy bonus is because its a hidden value. Unless its changed in a patch as i said. But the + bonus you see when you hover over a race is normally from a tech or similar effect. Hope that helps

well which bonus is it then? Im only going from memory of what paul said in may :/

I assume it is correct then that is just lowers the relationship degradation rate as Paul said, from memory at least. (The <<< arrows on the race window) And i assume , if your correct about the techs being the same, that it also does the same for those to. Although Im not personally sure about the techs being the same, but i haven't really looked into it for a long time..

If anyone can find the question being asked in the Live Stream video im sure it will give us more insight. Its one of the live streams not long after the ~30th of May. I skimmed though them but i couldn't find it, then again the video was missing aprox the first 10 mins of the stream so maybe it was cut out. Unless maybe the old Vod is still on there twitch page but i doubt it :/

EDIT: that being said it is entirely possible that Paul was wrong, or that the bonus itself is broken haha

I have done a serious late game diplomacy build with upgraded diplo buildings on every planet a few times.  It is my subjective opinion that it changes diplomacy significantly, making overall attitudes more positive.  After being DOWed by 7 out of 7 factions and fighting protracted wars, I was able to settle for peace, build diplo buildings, and then build alliances later.  I won't say it was easy, just the extreme approach I took to diplomacy, but it did seem to work effectively if you were patient.