Frank or Latin is the general term for most Western Europeans in the game setting. They are a diverse lot, presenting a multitude of ethnicities and the whole range of social status.
Franks will be from the Civilized background, with a wide range of careers representing the growing societies of the 13th Century.
Frank's of the Gentry rank and above will have funded (or had the clout/credit to borrow the money) their trip to the holy land. They will possess enough income to have at least one servant, as well as arms and equipment fitting their career, if any. Gentry and above can take a cultural combat style involving purely military weapons, a common example being Frankish Knight "Lance, Sword, Kite Shield" Combat Styles: Mounted Combat or Beast Back Lancer. This represents the training a nobleman would be given growing up to be groomed for warfare. All careers are open to Gentry or above without extra explanation, though careers as merchants or in manual laborers would warrant interesting character backgrounds. One important aside: unless the player is a member of the church it's highly unlikely that they know how to read; Even among the upper aristocracy literacy is low. Passions for upper-class Franks might be "Loyalty to Feudal Oath" or to a particular individual or family. Characters with exceptional faith might believe they have a higher calling to Crusade which could be represented by a passion, or be anxious to gain penance for evil deeds they have committed beforehand.
Lower-classes than Gentry in the holy land are likely poor pilgrims that have relied upon the church and kindness of others to reach their destination. They will have little with them in terms of wealth, certainly no more than a token weapon for defense if any at all. Cultural combat styles might be Levy or Hunter (Sling/Short Bow, S. Spear, and Round Shield ) Combat Style traits like Skirmishing or Ranged Marksman would not be inappropriate, representing a dedicated hunter or even poacher. It is highly unlikely that lower class Franks will be Agents, Alchemists, Courtiers, Merchants, Officials, Physicians or Scholars. Lower class Franks can enter the priesthood but will likely be barred from higher office due to competition from the upper classes. Warriors will be in a similar situation, a more appropriate title likely being "Bandit or Mercenary" though some may be well-to-do enough to be members of a knights retinue as a "man-at-arms" or "Serjeant" though they would be in poor economic straits if they were. Unless a member of the church, lower classes almost certainly do not know how to read.
The largest number of Franks are ,appropriately ,from France. Players can have a vague sense of where they are from regionally and not deal with anymore undue strife about their background. It is important to remember though that the notion of unified states does not exist for the majority of most Franks. The duke or lord of the area you lived/worked is much more important and real to you than the lofty King of France. Very often, rival Franks will fight one another over land rights and old feuds that will drag more and more of their counties down with them until a higher power steps in to arbitrate or forcefully settle the dispute.
There is also a sizable contingent of Italians in the holy land. Which city or region you hailed from from should be part of your characters background, and whether they support the Pope or the Holy Roman Emperor in the recent series of conflicts is also important.
The English, Spanish, Low-Countrymen and everything in-between have just as many complex social and cultural elements as the previously mentioned groups, but besides English animosity towards the French and Spanish dislike of Saracens (If your character has encountered any Moors in their past) they are not necessary as part of a characters background.
Note Those Franks interested in joining one of the Holy Orders wil get more information in the next section but the basic premise of Frankish society apply; the Orders do not train Knights/Sergeants, they recruit existing one's and add a layer of piety and discipline over their training.
Saracen is a broad term used by Franks to describe the more hostile local inhabitants of the holy land, just as Saracens use Frank to refer to most Westerners. Armenians are distinct in their own section. Otherwise, Saracens are assumed to be Muslims, which may be ethnically Syrian, Persian, Arab, Turag, or a number of other peoples. For the sake of brevity the complex distinction between the aforementioned groups is simplified for the players benefit.
Turks are distinct from Saracen's in enough ways culturally to warrant their own category. Turk can refer broadly to any number of nomadic peoples that dwell in Anatollia, the Caucasus, or the steppes around the Caspian or Aral sea and beyond. Turks are usually best represented by the nomadic culture, possibly barbarian depending upon geographic area. Turks that have become slaves to one civilized culture or another should still take the cultural background they spent their formative years in, layering on a career that they were enslaved to perform.
Greek is a broad term not only for natives to Greece but also to citizens or the former Eastern Roman Empire. Though many of these people can comfortably claim to be modern Romans, the Greek language and certain cultural ideas have overtaken old Latin elements, hence their denotation. Most Greeks will come from the civilized background, hailing from one of the longest, settled civilizations in the West.
Germans are distinct enough from Franks to warrant their own category, though many Saracens and Turks would not necessarily pay that much mind. Germans are distinct in that they inhabit a region with it's own confusing and violent social order, which is nominally united by a monarch that claims to harken back to the days of Charlemagne. German social order parallels that of the Franks, with an important distinction being that the upper nobility have a slightly different view of their overlord which could put them in conflict with the interests of the Catholic Church in this game's setting.
There are a huge variety of other cultures and nations that a character could choose from. Represented above are the most common or expected ethnic and their appropriate cultural backgrounds. These should not be seen as the only options for players, but they are recommended because the majority of the research that went into creating this game was done using sources from several of the previously mentioned groups. It's entirely possible for the players to be Russian nobleman or Hungarians on Crusade, Sudanese or other sub-Saharan groups brought to the Holy Land for trade or by force, or even Mongols that are under the employ of a local lord. So long as the GM is notified in advance of an interest to play a more exotic character and they fit in reasonably well with the rest of the group, accommodations can be made.