$ cd workingdirectory
$ perl6-m ../copyfnameascii.pl project copy

$ tree
                             .
                             ├── copy
                             │   ├── folder 1
$ tree                       │   │   ├── cr.txt
.                            │   │   └── es.txt
└── project                  │   └── folder 2
    ├── folder%201           │       ├── ai.txt
    │   ├── čř.txt           │       └── zy.txt
    │   └── ěš.txt   ~*>     └── project
    └── folder%202               ├── folder%201
        ├── áí.txt               │   ├── čř.txt
        └── žý.txt               │   └── ěš.txt
                                 └── folder%202
                                     ├── áí.txt
                                     └── žý.txt

use Inline::Perl5;
my $p5 = Inline::Perl5.new;
$p5.use('Text::Unidecode');

sub transformdirname($dirname is copy) {
  $dirname.=subst( /:i %(<[0..9A..F]>**2) /, { chr(:16(~$0)) }, :g ); # undo URL encoding
  $dirname.=subst( ///, '_', :g ); # make it a valid UNIX filename
  return $dirname;
}

sub transformfilename($filename) {
  return $p5.call('Text::Unidecode::unidecode', $filename); # make it ASCII at all costs
}

sub MAIN($fromdir, $todir) {
  for dir($fromdir) -> $subdir {
    unless $subdir ~~ :d {
      next;
    }
    my $tosubdir = $todir ~ '/' ~ transformdirname($subdir.basename);
    say $tosubdir;
    mkdir($tosubdir);
    for dir($subdir) -> $file {
      my $tofile = $tosubdir ~ '/' ~ transformfilename($file.basename);
      if $tofile.path ~~ :e {
        die("Will not overwrite $tofile");
      }
      copy($file, $tofile);
    }
  }
}

use Inline::Perl5;
my $p5 = Inline::Perl5.new;
$p5.use('Text::Unidecode');
.
.
sub transformfilename($filename) {
  return $p5.call('Text::Unidecode::unidecode', $filename);
}

use Text::Unidecode:from<Perl5>;

sub transformfilename($filename) {
  return Text::Unidecode::unidecode($filename);
}

sub transformdirname($dirname is copy) {
  $dirname.=subst( /:i %(<[0..9A..F]>**2) /, { chr(:16(~$0)) }, :g );
  $dirname.=subst( ///, '_', :g );
  return $dirname;
}

sub transformdirname($_ is copy) {
  .=subst( /:i %(<[0..9A..F]>**2) /, { chr(:16(~$0)) }, :g );
  .=subst( ///, '_', :g );
}

sub transformfilename($filename) {
  return $p5.call('Text::Unidecode::unidecode', $filename);
}

sub transformdirname($dirname is copy) {
  $dirname.=subst( /:i %(<[0..9A..F]>**2) /, { chr(:16(~$0)) }, :g ); # undo URL encoding
  $dirname.=subst( ///, '_', :g ); # make it a valid UNIX filename
  return $dirname;
}

#| undo URL encoding and make it a valid UNIX filename
sub transformdirname($_ is copy) {
  .=subst( /:i %(<[0..9A..F]>**2) /, { chr(:16(~$0)) }, :g );
  .=subst( ///, '_', :g );
}

say &transformdirname.WHY;

sub MAIN($fromdir, $todir) {

use Text::Unidecode:from<Perl5>;

# undo URL encoding and make it a valid UNIX filename
sub transformdirname($_ is copy) {
  .=subst( /'%' (<xdigit>**2)/, { chr(:16(~$0)) }, :g );
  .=subst( ///, '_', :g );
}

sub MAIN ($fromdir, $todir) {

  for dir $fromdir {

    next unless .d;

    say my $tosubdir = "$todir/&transformdirname(.basename)";
    mkdir $tosubdir;

    for dir $subdir {
      # make filename ASCII at all costs:
      my $tofile = "$tosubdir/{.basename.&Text::Unidecode::unidecode}";
      die "Will not overwrite $_" if $tofile.path.e;
      copy $_, $tofile;
    }
  }
}