How many languages are covered by Unicode?

It's hard to say. Many scripts (especially Latin) are used for a very large number of languages. The easiest answer is that Unicode covers all the languages that can be written in the following scripts: Latin, Greek, Cyrillic, Armenian, Hebrew, Arabic, Syriac, Thaana, Devanagari, Bengali, Gurmukhi, Oriya, Tamil, Telugu, Kannada, Malayalam, Sinhala, Thai, Lao, Tibetan, Myanmar, Georgian, Hangul, Ethiopic, Cherokee, Canadian-Aboriginal Syllabics, Ogham, Runic, Tagalog, Hanunóo, Buhid, Tagbanwa, Khmer, Mongolian, Limbu, Tai Le, Han (Japanese, Chinese, Korean ideographs), Hiragana, Katakana, Bopomofo, Yi, Linear B, Old Italic, Gothic, Ugaritic, Deseret, Shavian, Osmanya, and Cypriot.. See also the list of Languages and their Scripts