Use a negative width to left-justify. For example,
"%5s" means pad to 5 characters, right-justified.
"%-5s" means pad to 5 characters, left-justified.

The following are not the most compact solutions, but they are probably the most readable. Don't forget that programs should be written for those who maintain them.

Untransposed:

use strict;
use warnings;

use List::Util qw( max );
use POSIX      qw( ceil );

my @a = qw(un deux trois quatre jedan dva tritcheteri one two three);
my $cols = 4;

my $width = (max map length, @a) + 1;
my $rows = ceil(@a / $cols);

for my $r (0..$rows-1) {
   for my $c (0..$cols-1) {
      next if (my $i = $r * $cols + $c) > $#a;
      printf('%-*s', $width, $a[$i]);
   }
   print("\n");
}
[download]

Transposed:

use strict;
use warnings;

use List::Util qw( max );
use POSIX      qw( ceil );

my @a = qw(un deux trois quatre jedan dva tritcheteri one two three);
my $cols = 3;

my $width = (max map length, @a) + 1;
my $rows = ceil(@a / $cols);

for my $r (0..$rows-1) {
   for my $c (0..$cols-1) {
      next if (my $i = $r + $c * $rows) > $#a;
      printf('%-*s', $width, $a[$i]);
   }
   print("\n");
}
[download]

Now, wouldn't it be nice if each column was as narrow as possible? There's gotta be a module to do that on CPAN, but I didn't find one quickly.

Update: I had to leave before I could finish writting my entire node. Here's the rest.

Update: Fixed a bug in "Transposed". Thanks to jhourcle for pointing it out.