I'm not sure what your ENV looks like etc but this works; fix-uri=no|0
is all that was required for me. I added the char-encoding
argument for good measure. Perl's tidy wraps the tidy lib so this should be valid for most/any tidy use after converting the arguments.
#!/usr/bin/env perl
use strictures;
use utf8;
use open qw( :std :utf8 );
use HTML::Tidy;
print HTML::Tidy
->new({ "show-body-only" => 1,
"char-encoding" => "utf8",
"fix-uri" => 0, })
->clean(q{<a href="http://www.äöü.com/">Link</a>});
__END__
<a href="http://www.äöü.com/">Link</a>