New OS and App localizations: Arabic, Czech, Hungarian, and Turkish. These bring the total to 22.
New languages supported with both fonts and keyboards: Bangla, Georgian, Kannada, Khmer, Kurdish, Malayalam, Myanmar, Oriya, Sinhala, Telugu, Urdu. These have about 600 million speakers all together.
New languages/scripts supported with fonts only: Ethiopic/Amharic, Lao, Emoji
New languages supported via voices: Arabic, Chinese, Czech, Danish, Dutch, Finnish, French, German, Greek, Hindi, Hungarian, Indonesian, Italian, Japanese, Korean, Norwegian, Polish, Portuguese, Romanian, Russian, Slovak, Spanish, Swedish, Thai, Turkish. These must be downloaded separately.
New Spellcheckers: None
Other new features: Support for vertical text in TextEdit, access to accented characters via a pop-up dialogue when you hold down a character, improved Chinese, Japanese, and Vietnamese input methods, British English modules in Dictionary.app, support for Windows Indic fonts in TextEdit.