ICU still depends on libc for compatibility with certain historical behavior for single-byte encodings. Make the dependency explicit by holding a locale_t object when required. We should consider a better solution in the future, such as decoding the text to UTF-32 and using u_tolower(). That would be a behavior change and require additional infrastructure though; so for now, just avoid the global LC_CTYPE dependency. Reviewed-by: Chao Li <li.evan.chao@gmail.com> Discussion: https://postgr.es/m/450ceb6260cad30d7afdf155d991a9caafee7c0d.camel@j-davis.com