D.6 Predefined Macros for Unicode support
There are two macros that can help you write scripts that work for both Unicode and ANSI installers. To figure out if the script is being compiled to generate a Unicode installer, use !ifdef to check for ${NSIS_UNICODE}. To see what the size of a character is, use ${NSIS_CHAR_SIZE}. It will be 1 for ANSI and 2 for Unicode installers.