I once saw that i was receiving gold from "Foreign civilizations" so i assumed it was trade...but it was probably just tribute.
It's really sad that civ 5 is missing a lot of "must have" mechanics from older games...
Well, this is pretty much the only one, to be fair. It misses a few minor Civ IV introductions (health, corporations, vassals/colonies, UN resolutions, random events), but in terms of general mechanics from the older games there's foreign trade, map trading, and that's essentially it.
Trade & commerce has always been underplayed in ALL civ versions, but atleast civ4 made a go of it (Astronomy opened up international trade routes, Custom House increased Trade yield, Privateers could blockade non-hostile Civs, Diplomancy affected trade/revenue and vice versa....etc). Far from perfect but it was a serious Game Feature to go along with Warfare, Conquest, Diplo, Religion, Espoinage, Health and so on.
I wouldn't say there was anything particularly wrong with Civ IV's foreign trade mechanic, however thinking on it I can see reasons why foreign trade would have been removed in Civ V:
Civ V is permeated by one design philosophy: Tall vs. wide. Trade is part of that trade-off - wide civs benefit more from trade routes. Allowing international trade would give tall empires the same advantages, blurring the distinction Civ V is founded on (although they could obviate this by doing what Civ IV did, and set a cap on the number of trade routes a single city can maintain).
Gold is much more important in Civ V than in prior Civ games; greater numbers of trade routes = easier access to gold = easier game.
I'm not convinced either is a particularly good or insurmountable reason, but it may be an explanation for a mechanical change that otherwise seems arbitrary. And with mechanics like Macchu Picchu and Messenger of the Gods, it's unlikely that a future expansion will restore foreign trade - trade routes are simply more powerful in Civ V than in the older games, so require a cap of some kind.
Civ V should fix the problem where you can get all of a civ's gold by trading away everything, then DoW DVD get it all back. Right now it's advantageous to start wars.
This was always possible in Civ, since the AI doesn't know you plan to declare war on it, it was just less advantageous in earlier games because gold wasn't particularly valuable - it was just there to allow you to maintain more cities/units. The best way to fix it is to improve the AI so that it just doesn't keep enough spare gold to make this a viable approach. However, they should also add a "You declared war on a trade partner" negative modifier that kicks in if you declare war on an AI before the trade deal is up.
Good relations with other civs should result in benefits, not just trading luxuries or research agreements.
But this has never been the case in Civ. Trade in Civ IV, for instance, was a way of cultivating good relations - practically anyone would trade with you if you weren't at war. The benefits you got from trade weren't from having "good relations", they were just from not being at war. There are plenty of benefits to good relations with other civs in Civ V, but these are diplomatic benefits - greater prospects for allies in war, defensive pacts, forming blocs likely to denounce rival powers. And, yes, sometimes you can ask for free gold or luxes. In that, Civ is leagues ahead of prior Civ games and that's the primary benefit good relations should have. Where you fall along the sliding scale (i.e. how much they like or dislike you) now matters, whereas in the past it was pretty binary - you were either at peace and reaping benefits, or at war.
None of which is to disagree that foreign trade benefits should be better-incorporated into Civ V, but the removal of foreign trade hasn't made diplomatic relations less meaningful.