ISO/IEC 8859-9
ISO/IEC 8859-9:1999, Information technology — 8-bit single-byte coded graphic character sets — Part 9: Latin alphabet No. 5, is part of the ISO/IEC 8859 series of ASCII-based standard character encodings, first edition published in 1989. It is designated ECMA-128 by Ecma International and TS 5881 as a Turkish standard. It is informally referred to as Latin-5 or Turkish. It was designed to cover the Turkish language, designed as being of more use than the ISO/IEC 8859-3 encoding. It is identical to ISO/IEC 8859-1 except for the replacement of six Icelandic characters with characters unique to the Turkish alphabet. And the uppercase of i is İ; the lowercase of I is ı.
ISO-8859-9 is the IANA preferred charset name for this standard when supplemented with the C0 and C1 control codes from ISO/IEC 6429. In modern applications Unicode and UTF-8 are preferred; authors of new web pages and the designers of new protocols are instructed to use UTF-8 instead. Since 2023, less than 0.05% of all web pages use ISO-8859-9, while 2.1% of web pages located in Turkey declare use of ISO-8859-9. However, the WHATWG Encoding Standard, which specifies the character encodings which are permitted in HTML5 and which compliant browsers must support, requires that web pages marked as ISO-8859-9 be handled as Windows-1254, which differs from ISO-8859-9 by using the CR range which ISO-8859-9 reserves for C1 control codes for additional graphical characters instead.
Microsoft has assigned code page 28599 a.k.a. Windows-28599 to ISO-8859-9 in Windows. IBM has assigned code page 920 to ISO-8859-9. It is published by Ecma International as ECMA-128.