.tr -\(hy .TL Hello World .br or .br Καλημέρα κόσμε .br or .br こんにちは 世界 .AU Rob Pike Ken Thompson .AI .MH .AB Plan 9 from Bell Labs has recently been converted from ASCII to an ASCII-compatible variant of Unicode, a 16-bit character set. In this paper we explain the reasons for the change, describe the character set and representation we chose, and present the programming models and software changes that support the new text format. Although we stopped short of full internationalization\(emfor example, system error messages are in Unixese, not Japanese\(emwe believe Plan 9 is the first system to treat the representation of all major languages on a uniform, equal footing throughout all its software. .AE .SH Introduction .PP The world is multilingual but most computer systems are based on English and ASCII or worse. The pending release of Plan 9 [Pike90], a new distributed operating system from Bell Laboratories, seemed a good occasion to correct this chauvinism. It is easier to make such deep changes when building new systems than by retrofitting old ones. .PP The ANSI C standard [ANSIC] contains some guidance on the matter of `wide' and `multi-byte' characters but falls far short of solving the myriad associated problems. We could find no literature on how to convert a .I system to larger character sets, although some individual .I programs have been converted. This paper reports what we discovered as we explored the problem of representing multilingual