Unicode is a format which can simultaneously encode characters from languages across the world: Arabic, Chinese, Greek, Hebrew, Japanese, Roman, Russian, and a host of others. Cocoa can produce Unicode, so TeXShop can as well. To experiment, open the International preference in the System Preferences program, choose the Input Menu tab, and add additional selections to the items already selected. It is illuminating to select Greek (because it is familiar), Hebrew (because it is written from right to left), Arabic (because it is written from right to left and makes extensive use of ligatures, so characters have different shapes at the ends of words than in the middle) and Chinese. A new menu item will appear with a flag indicating the current input language.

Type some characters, switch to another language, and type some more.

There are several formats for Unicode files. A preference item allows users to select two of them. Standard OSX Unicode is the usual code used by Mac OSX, but I do not know if this is useful in the TeX world. UTF-8 Unicode is a popular format because ordinary ascii characters appear as they usually do. If a file is saved in UTF-8 format, TeX can process it, but it will convert Unicode characters to question marks.

There is a TeX package which accepts UTF-8 Unicode input files; see

  `http://www.ctan.org/tex-archive/macros/latex/contrib/supported/unicode/`

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Unicode