Since availability of languages is dependent upon Unicode, it would be best to answer this question in Unicode terms from the Unicode site. 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; Telegu; Kannada; Malayalam; Sinhala; Thai; Lao; Tibetan; Myanmar; Georgian; Hangul; Ethiopic; Cherokee; Canadian-Aboriginal Syllabics; Ogham; Runic; Khmer; Mongolian; Han (Japanese, Chinese, Korean ideographs); Hiragana; Katakana; Bopomofo and Yi.
A complete list of covered languages is available at the link below;