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There is a build-time option to replace the system's wide-character ‘wctrans’ C function by tables shipped with R: use ‘configure’ option ‘--with-internal-towlower’ or (on Windows) ‘-DUSE_RI18N_CASE’ in ‘CFLAGS’ when building R. This may be needed to allow ‘tolower()’ and ‘toupper()’ to work with Unicode characters beyond the Basic Multilingual Plane where not supported by system functions (e.g. on Solaris where it is the new default).