FF Unit Slab supports 164 different languages such as Spanish, English, Portuguese, Russian, German, French and Greek in Latin, Cyrillic, and Greek scripts. (Please note that not all languages are available for all formats.)
When Christian Schwartz and Erik Spiekermann were working on the design for FF Meta Serif, they also had plans to design FF Unit Slab—either at the same time, or right after FF Meta Serif would be released. They figured that, as FF Meta and FF Unit have so much in common, it would be smart to make two serif families that could be used together as well, along with either of the sans serifs. FF Meta, which has more organic details, was going to be the more traditional serif text face. FF Unit seemed like it would adapt well to being a clean and contemporary slab serif, especially since the i and I in the sans already showed them what the serifs would look like. Christian Schwartz worked together with Kris Sowersby to rough out complete ranges of test-words for both families at the same time, and FF Unit Slab sat half-finished while FF Meta Serif was completed.
FF Unit Slab is a fairly condensed slab which pulls a punch in bold headlines and looks surprisingly good in text with its typewriter-like discipline. FF Unit Slab can be mixed with FF Unit, of course, but also works as companion to FF Meta, while FF Meta Serif looks good when mixed with FF Unit—whether for headlines or small text like captions. The two families share a common heritage and like to hang out with each other.