How does different races in the Warhammer fantasy universe interact with each other.

[Desmond]

I know humans,elfs,dwarfs trade and has dialogs with eachother well not so much elfs and dwarfs anymore.

Marionburg pretty much trades with whoever.
In Mark of Chaos the skaven worked for chaos a while. and Dark elfs used Greenskin a while. So they do speak

[zefyris]

For High elves, they didn't had any real contact with old world races for a very long time, until the previous Phoenix King changed that, sending Finubar the seafarer here and there in the world to renew contact with the various races, and such activity continued after Finubar became Phoenix King.

They took contact with the various human kingdoms, but also with the dwarves (first time since the war of the beard), and I believe that they tried again with the wood elves but I don't know if wood elves accepted to talk (last time they tried before Finubar, wood elves trapped for decades the HE ambassadors in the forest before having it exit the forest, without seeing them at all. They actually were killed by angry Brettonians armies right after exiting the forest).
Their only contact with chaos, Norsca, greenskins and Dark elves is through war. I don't think they really have contact with anything else. Skavens don't come to Ulthuan, Lizardmen are not keeping active contact with anyone AFAIK, vampires and tomb kings don't really have any relations with elves and other races are simply too far away to begin with.

Teclis, Yrtle and i don't remember who was the third mage spent quite a while on the Empire's soil, helping them to push back the Chaos invasion, and then creating the various magic academies (colleges of magic in english?) to allow humans to use magic and defend themselves before returnign to ulhuan (well, the two that survived, that is).

Obviously when the language is different, their ambassador are usually able to speak the other language, but I don't think that many other peoples are bothering with that.