perllocale does mention the fact that it ignores the external locale unless set in the script.

use locale;
use POSIX qw(locale_h);
setlocale("LC_ALL", "fr_FR.ISO8859-1"); 
print uc("â, ê, î, ô, û\në, ï, ü\nà, è, ù\nç\næ\nécriture complis\n");
+'
...
Â, Ê, Î, Ô, Û
Ë, Ï, Ü
À, È, Ù
Ç
Æ
ÉCRITURE COMPLIS
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