But would we really all "be speaking German" had the Nazis won? I think that the emphatic answer to this is no (the combined British and American fleets would have stopped any German invasion attempt). But what WOULD a plausible post-World War II Nazi world look like?
For the sake of simplicity (mainly since it affects how the post-war map would be drawn), I'm going to drastically streamline what it would have taken for Germany to win the war. Two pivotal battles, Stalingrad and El Alamein in 1942, would prove to be the turning point of the war in many respects in hindsight. So let's assume that the Germans actually win both of those battles. It could be due to any reason, the fortunes of war, bravery in combat, superior leadership, etc.
Assuming victories in those two battles allows for the possibility of the following to happen: With a victory at Stalingrad, Germany pushes further into the Russian steppe and eventually reaches the oil fields of Caucasus. With oil in hand and morale high, the Germans continue to push into Russian territory. In the Middle East, the German-Italian victory at El Alamein propels Rommel into Alexandria. Playing off of the frustrations of Arabs living under British colonial rule, Rommel continues to push into the middle east with their support, eventually linking up with German forces in Russia in the Caucasus mountains. These two successes result in an uptick of support for Mussolini and Italy remains in the war (they historically exited in 1943). With Italian support, Vichy France is able to defend against Operation Torch, and in turn Italy is never invaded.
German successes in Russia continue and eventually Moscow falls. Eventually the front turns into a stalemate, but the abundance of resources captured and the fact that Italy remains free from invasion results in enough German forces to properly man the "Atlantic Wall", thus preventing any discussion a D-Day type landing and further allowing Germany to focus on the Eastern front.
In the Pacific theater, things proceed historically (The Pacific theater was in many ways its own war, and what happened in Europe had little appreciable effect in the Pacific). Things proceed historically until after Japan is nuked twice and forced to surrender. At this point, the Soviets can be assumed to still be focused on Germany, and would not be able to historically invade Manchuria and North Korea. With this in mind, American forces land en masse in Korea, taking the whole peninsula.
With the Japanese surrender, Chiang Kai-Shek is able to occupy Manchuria and take possession of the heavy industrial machinery that historically the Soviets stole for their own use. Buttressed by the heavy industry in Manchuria and with American support in Korea ready to assist him, Chiang Kai-Shek is able to defeat the Communists and Mao Zedong is relegated to the pages of history.
At the same time, the weakened state of Russia presents both China and the U.S. a unique opportunity. With American assistance (which might seem odd at first glance given the historical WW2 relationship, but in fact it makes perfect sense -- the U.S. never liked the Soviets, and even sent troops after World War 1 to assist the White Russians fighting the Bolsheviks), China attacks Russia and captures Mongolia and Primorsky, historcal territories of the Qing dynasty. Now under attack from the east as well as the west, Russia folds to both Nazi and Sino-American demands.
With both Japan and the Soviets out of the war, the Western appetite for further conflict wanes considerably. A second Sitzkrieg envelops the European front, with Germany lacking the navy to attack and invade Britain and/or the U.S. By this time, assuming its around 1946, and with little willingness to nuke Germany due its relative strength (Germany in this position, unlike Japan, would be in a very strong position with many allies) and Germany's own development of the bomb, the Allies decide to go to the peace table with the Germans and Italians, resulting in this:
The darker variant of the color represents the direct control of a country, while the lighter color represents a puppet state/protectorate/satellite state. It is assumed here that the colonies of Vichy France, cutoff from France proper and with the Axis having no available means of reclaiming them (i.e. lack of naval superiority) would be ceded to or become de facto British possessions (likewise with Belgian Congo). Dutch Indonesia would likely become independent due to its insular and more removed nature.
China (under Republican control) would gain possession of Mongolia, Primsorky and Tibet (invading it while the Western powers sit idly by as they did with Communist China). Japan, all of Korea, and the Philippines would be under American control until independence would be granted. Greenland and Denmark would become U.S. possessions, gaining them from cutoff Denmark (historically they occupied them during the war and then gave them back).
Italy would receive the historically Italian town of Nice as well as the colonies of Morocco, Algeria and Tunisia, from an isolated Vichy France, while it would demand and receive claim over much of the Middle East and East Africa from the British (due to its entrenched military control with German assistance).
Russia's concessions to the Allies would be the aforementioned cession of Mongolia and Primorsky to China, as well as the granting of independence of its Central Asian Soviet Republics (which would quickly fall under the sway of Chinese influence). To Germany, Russia would cede Ukraine, Belorussia, the Baltic states, and the entirety of the Caucasus region. To Finland, Russia would cede Karelia and the surrounding territory, fulfilling a historical Finnish claim to these lands.
Germany itself would create satellite and puppet states in the Balkans and Eastern Europe (much like the Soviets did) as well as in Iran (which would not be invaded and put under joint Anglo-Soviet control as it was historically). It would also doubtlessly annex Alsace-Lorraine from France, as well Luxembourg, Ukraine and the Baltic states and surrounding areas, both for resources as well as lebensraum ('living space'). It would leave some areas, like Belorussia, as nominally independent as a matter of administrative efficiency. The dreams of a Greater Germany or Grossdeutschland would be realized.
So what would have happened after the dust had settled? Probably a sort of Cold War between Nazi Germany and the U.S., Britain as well as China, not much different from the historical Cold War. Russia, surrounded by hostile nations and having lost much of its best territory, would be relegated to regional power status along with France. Britain's empire would probably fall apart as it did historically.
For fun, I decided to look at the areas I've added to Germany and come up with modern GDP and population numbers. Using today's census numbers, this theoretical Greater Germany would have a population of 159,582,604 (almost exactly twice that of Germany's current population of 81,802,000) and a GDP of $4,093,670,000,000 (a 24% increase from Germany's current GDP). Greater Germany's population would rank 7th in the world, behind China, India, America, Indonesia, Brazil and Pakistan, and its GDP would rank 4th as it does now, though the gap between it and Japan at 3rd would be significantly reduced.
Obviously this is pretty flawed, since the development of these regions would have been vastly different, for better or for worse. Given the traditional strength of the German economy, these regions under German control would have probably been higher both in population and in terms of GDP than they are today.
Either way, it's fun food for thought.