use strict;
my $str = '# Test is a cool word {{source|{{nom w pc|Chantal|Bouchard}}, \'\'La langue et le nombril\'\', Presses de l\'Université de Montréal (PUM), 2020, p. 174}}.
# Test is a cool word {{source|Nicolas|Daniel, Presses de l\'Université de Montréal 4}}';
my $regex = qr/\s*\{\{source\|(?>[^{}]|(\{\{(?:[^{}]++|(?1))*}}))*}}\s*/mp;
my $subst = '';
my $result = $str =~ s/$regex/$subst/rg;
print "The result of the substitution is' $result\n";
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html