What does this output:

<?php
if (false !== setlocale(LC_ALL, 'lv_LV.UTF-8')) {
  $locale_info = localeconv();
  var_dump($locale_info);
}
?>

Output requested:

array(18) {
  ["decimal_point"]=>
  string(1) ","
  ["thousands_sep"]=>
  string(2) "��"
  ["int_curr_symbol"]=>
  string(4) "LVL "
  ["currency_symbol"]=>
  string(2) "Ls"
  ["mon_decimal_point"]=>
  string(1) ","
  ["mon_thousands_sep"]=>
  string(2) "��"
  ["positive_sign"]=>
  string(0) ""
  ["negative_sign"]=>
  string(1) "-"
  ["int_frac_digits"]=>
  int(2)
  ["frac_digits"]=>
  int(2)
  ["p_cs_precedes"]=>
  int(1)
  ["p_sep_by_space"]=>
  int(1)
  ["n_cs_precedes"]=>
  int(1)
  ["n_sep_by_space"]=>
  int(1)
  ["p_sign_posn"]=>
  int(3)
  ["n_sign_posn"]=>
  int(3)
  ["grouping"]=>
  array(2) {
    [0]=>
    int(3)
    [1]=>
    int(3)
  }
  ["mon_grouping"]=>
  array(2) {
    [0]=>
    int(3)
    [1]=>
    int(3)
  }
}

The "garbage" you get is a non-breaking space in UTF-8. You can always use utf_decode() on it:

<?php
if (false !== setlocale(LC_ALL, 'lv_LV.UTF-8')) {
    $locale_info = localeconv();
    echo number_format(20000,0,$locale_info['decimal_point'],
utf8_decode($locale_info['thousands_sep']));
}
?>

Since unicode support is coming in PHP6 and will not be addressed before, this is "wont fix" in earlier versions.

I suggest you really don't use setlocale() if you want to use UTF-8.
At least not for numbers.

Thanks for the tip.

You may also want to look at http://pecl.php.net/package/intl