# note: system locale works properly
$ LC_CTYPE=fi_FI.UTF-8; export LC_CTYPE

# WITH use locale:
$ perl -CSA -e 'use utf8; use open ":std", IO => ":utf8"; use locale; use POSIX qw(locale_h); print "LC_CTYPE: ", setlocale(LC_CTYPE), "\n"; $str = "säv sov san"; my @arr = $str =~ /\b(\w{3})\b/g; print "", join("|", @arr), "\n";'
LC_CTYPE: fi_FI.UTF-8
sov|san

# WITHOUT use locale:
$ perl -CSA -e 'use utf8; use open ":std", IO => ":utf8"; use POSIX qw(locale_h); print "LC_CTYPE: ", setlocale(LC_CTYPE), "\n"; $str = "säv sov san"; my @arr = $str =~ /\b(\w{3})\b/g; print "", join("|", @arr), "\n";'
LC_CTYPE: fi_FI.UTF-8
säv|sov|san