By default, perl assumes that your source code is in LATIN-1

By default, perl assumes that your source code is in ASCII. (Though string literals are 8-bit clean.)

$ printf 'use utf8; sub bête { } say "ok";' | perl -M5.010
ok

$ printf 'sub bête { } say "ok";' | iconv -t iso-8859-1 | perl -M5.010
Illegal declaration of subroutine main::b at - line 1.
[download]