use strict;
use warnings;

my $BEL_LETTERS = qr/ABVHD/;
my @all_words = qw(tak het hen toj tah tam tym);

...

while (my $next_line = <$FH>) {
    foreach my $next_word (@all_words) {
        my $count_words =
           ($next_line =~
           s/\b($next_word[$BEL_LETTERS]*)\b/>$1</gi);
    }
}