my $re_langs = sprintf '(?:%s)', join '|', keys %validLanguages;

##</code><code>##

  $text =~ /^(?:$re_langs|\s|,)*\z/;

##</code><code>##

  $text =~ /^(?:$re_langs(?=\s|,|\z)|\s|,)*\z/;

##</code><code>##

  $text =~ /^(?:$re_langs\b|\s|,)*\z/;

##</code><code>##

  $text =~ m{
    ^
    (?: $re_langs \b
      | \s
      | , (?! \s*, ) # comma not followed by another comma
                     # (not even with intervening whitespace)
    )*
    \z
  }x;

##</code><code>##

  $text =~ m{
    ^
    \s* ( ,\s* )?  # allow stuff to precede first language
    (?: $re_langs
      (?: \s+
        | \s* , \s*
        | \z
      )
    )* \z
  }x;

##</code><code>##

  $text =~ /^\s*(?:$re_langs\s*(?:,\s*|\z))*\z/;