Also, if anyone could clarify what exactly specializing in world history means, that would be extremely helpful. It seems a little broad for a specialization.

To understand what world history is, you first have to have a little background in how history has been traditionally studied in the US since World War II. In order to prepare itself for its role as a global hegemon, the federal government issued funding for the creation and expansion of so-called area studies departments in universities across the country. These were meant to generate experts on the nuances of different regions of the world (Latin America, the Middle East, East Asia, etc.). Departments funded PhDs for regional specialists and hired professors to fulfill these roles. This had the effect of compartmentalizing the study of history. You had your historians of the Middle East, South Asia, East Asia, etc. but they didn't engage in many interdisciplinary studies. World history as a distinct field of study crystallized in the 1980s as an alternative to the area studies approach, by emphasizing the value of studying interconnections and comparisons between world regions. World historians would argue that you can't truly understand any part of the world in isolation, without understanding how it fits into a larger picture and relates to other parts of the world.

The significant thing to note here is that "world history" is not some watered-down version of all other narrow historical specializations conglomerated together. World historians use their more zoomed-out lens to spot things which otherwise might go unnoticed. Some famous examples include William McNeill's Plagues and Peoples, which explores the way that diseases have shaped human history and puts forward theories that explain patterns of outbreak. Another is Alfred Crosby's The Columbian Exchange, which demonstrates the global ecological and biological impact of the discovery of the New World in 1492 - the term has now become a household name. These books and others like them take a look at global processes which might not be apparent to anyone focusing their study on one specific area. Seventeenth-century economic downturn, rebellion, and state breakdown in Europe, China, and the Ottoman Empire takes on new meaning when one recognizes the commonalities between each of these regions, which is the argument of Geoffrey Parker in his Global Crisis: War, Climate Change and Catastrophe in the Seventeenth Century. World history allows one to identify long-term trends and processes, and to establish comparisons between societies across the globe. Thus it's an understandably broad field and can take a variety of forms, from the history of a single commodity (Molly Warsh, American Baroque: Pearls and the Nature of Empire, 1492-1700), to the study of trans-continental commercial networks (Sebouh David Aslanian, From the Indian Ocean to the Mediterranean: The Global Trade Networks of Armenian Merchants from New Julfa) to the environmental impact of human activity (J. R. McNeill, Something New Under the Sun: An Environmental History of the Twentieth-Century World), or even how human history looks when placed within the context of the history of the universe (David Christian, Maps of Time: An Introduction to Big History).

World history as a field is also generating a sustained critique of Eurocentrism. Twentieth-century narratives of the "history of the world" were very much centered on Europe and the West, emphasizing Europe's unique character and the supposedly intrinsic advantages that Europeans had over the rest of the world dating back centuries. For the past twenty years or so, an immense literature has been developing that challenges many of these assumptions, inspired above all by Andre Gunder Frank's ReOrient: Global Economy in the Asian Age (1998) and Kenneth Pomeranz's The Great Divergence: China, Europe, and the Making of the Modern World Economy (2000). World history is, in effect, helping to create a more balanced understanding of how Europe related to the rest of the world through the study of global interconnections and cross-regional comparison.

On world history as a discipline:

• Christian, David ed. The Cambridge World History. Vol 1: Introducing World History, to 10,000 BCE. Cambridge: Cambridge University Press, 2015.
• Manning, Patrick. Navigating World History: Historians Create a Global Past. New York: Palgrave MacMillan, 2003.
• Northrop, Douglas ed. A Companion to World History. Wiley Blackwell, 2012.

Language requirements will depend a bit on the department, so I would always ask or check their website and see if they have graduate requirements. The university I am at requires proficiency in two foreign languages in addition to English. You prove proficiency by either passing through the first two years worth of levels for any language or taking a placement test of some kind. However, American history specialists (along with anyone else who can make the case) need only have one additional language, but are expected to take a comprehensive exam in a specific theoretical historical approach (ethnographic, social, cultural, material, etc.)

If you can get started on languages early, more power to you. The fact that I already had fluency in a language aside from English gave me a head start. I had two other languages I had taken extensively as well (Italian and Japanese) but as neither of those had any bearing on my work I had to find a more potentially useful foreign language to fulfill my requirement. YMMV though, so as I said, check out the programs you might want to go to.

As to World History, I would highly suggest you check out the website for the World History Association and the Journal of World History. You don’t need to go off reading every single article, but look through those both; especially article titles and conference talk titles, and you should get a pretty good initial taste of the breadth and depth of the field. World Histories are very often transnational or transregional— they often cover movement of people, material, practices, capital, or ideas. They are sometimes very small, almost micro-histories, but are employed as examples for larger phenomena that are otherwise too vague and impersonal to research in an archive.

As a seasoned linguist I would certainly say French is key to an understanding of world history, simply due to the importance of French as a major lingua franca since the Middle Ages. German and Italian could also be said to be of similar importance, especially in Europe, whilst Spanish would certainly be useful when studying the Americas, especially if you're studying US history in California. Of those languages I would say Spanish is the easiest for native English speakers, but it would really depend on your particular specialisation, which essentially means pursuing a more specific subject in world history that you're interested in in greater detail, for example the impact of the US Civil War on the Egyptian cotton industry, or the development of Filipino national identity in the 19th century.

Is there a particular field of interest that you're leaning towards?