my $base_dir_abs = "/var/www/templates";
my $default_lang = 'en';
my $lang         = lc $ENV{'HTTP_ACCEPT_LANGUAGE'}
my @dirs = ("$base_dir_abs/$default_lang");

if ($lang
    && $lang ne $default_lang
    && $lang =~ /^(\w{2})/ # may look like "en-us"
    && -d "$base_dir_abs/$1") {
    unshift @dirs, "$base_dir_abs/$1";
}

my $tt = Template->new({
    INCLUDE_PATH => \@dirs
});
$tt->process($file);

OR

my $ht = HTML::Template->new(
    filename => $file,
    path     => \@dirs,
);