Unicode

Unicode is a computing industry standard for the consistent encoding, representation, and handling of text expressed in most of the world's writing systems. The latest version contains a repertoire of 136,755 characters covering 139 modern and historic scripts, as well as multiple symbol sets. The Unicode Standard is maintained in conjunction with ISO/IEC 10646, and both are code-for-code identical.
The Unicode Standard consists of a set of code charts for visual reference, an encoding method and set of standard character encodings, a set of reference data files, and a number of related items, such as character properties, rules for normalization, decomposition, collation, rendering, and bidirectional display order (for the correct display of text containing both right-to-left scripts, such as Arabic and Hebrew, and left-to-right scripts).^[1] As of June 2017, the most recent version is Unicode 10.0. The standard is maintained by the Unicode Consortium.
Unicode's success at unifying character sets has led to its widespread and predominant use in the internationalization and localization of computer software. The standard has been implemented in many recent technologies, including modern operating systems, XML, Java (and other programming languages), and the .NET Framework.
Unicode can be implemented by different character encodings. The Unicode standard defines UTF-8, UTF-16, and UTF-32, and several other encodings are in use. The most commonly used encodings are UTF-8, UTF-16 and UCS-2, a precursor of UTF-16.
UTF-8, dominantly used by websites (over 90%), uses one byte for the first 128 code points, and up to 4 bytes for other characters. The first 128 Unicode code points are the ASCII characters; so an ASCII text is a UTF-8 text.
UCS-2 simply uses two bytes (16 bits) for each character but can only encode the first 65,536 code points, the so-called Basic Multilingual Plane. With 1,114,112 code points on 17 planes being possible, and with over 120,000 code points defined so far, many Unicode characters are beyond the reach of UCS-2. Therefore, UCS-2 is obsolete, though still widely used in software. UTF-16 extends UCS-2, by using the same 16-bit encoding as UCS-2 for the Basic Multilingual Plane, and a 4-byte encoding for the other planes. As long as it contains no code points in the reserved range U+0D800-U+0DFFF, a UCS-2 text is a valid UTF-16 text.
UTF-32 (also referred to as UCS-4) uses four bytes for each character. Like UCS-2, the number of bytes per character is fixed, facilitating character indexing; but unlike UCS-2, UTF-32 is able to encode all Unicode code points. However, because each character uses four bytes, UTF-32 takes significantly more space than other encodings, and is not widely used.