i18n: use UTF-8 string to lower filename for case collision check Some character sets, cp932 (known as Shift-JIS for Japanese) for example, use 0x41('A') - 0x5A('Z') and 0x61('a') - 0x7A('z') as second or later character. In such character set, case collision checking recognizes different files as CASEFOLDED same file, if filenames are treated as byte sequence. win32mbcs extension is not appropriate to handle this problem, because this problem can occur on other than Windows platform only if problematic character set is used. Callers of util.checkcase() use known ASCII filenames as last component of path, and string.lower() is not applied to directory part of path. So, util.checkcase() is kept intact, even though it applies string.lower() to filenames.