Indeed, for string comparisons and substring searches, Unicode::Collate is the way to go.

use v5.40;
use utf8;
use open ':std', ':encoding(UTF-8)';

use Unicode::Collate qw( );

sub f { $_[0] < 0 ? "lt" : $_[0] > 0 ? "gt" : "eq" }

my $s1 = "voilą";  # Canonical spelling
my $s2 = "voila";  # Alternative spelling

my $collator = Unicode::Collate->new( ignore_level2 => true );

my $cmp = $collator->cmp( $s1, $s2 );

say "$s1 ".( f( $collator->cmp( $s1, $s2 ) ) )." $s2";
[download]

voilą eq voila
[download]

Unfortunately for the OP, while Perl's regex engine can ignore case, it doesn't support ignoring diacritics.