If you are dealing with i18n and client side effects, you might need an equivalent for the format_number_choice() helper in Javascript. Here is a simplified version:

function format_number_choice(text_string, replace_hash, number) {
  pattern = new RegExp("\\["+number+"\\]\s?([^\|]*)");
 
  function replace_in_string(text_string, replace_hash) {
    for(var i in replace_hash)
     text_string = text_string.replace(new RegExp(i), replace_hash[i]); 
    return text_string;
  }
 
  matches=text_string.match(pattern);
  if(matches != null)
    return replace_in_string(matches[1], replace_hash);
  else {
    pattern = /\[else\]\s?([^\|]*)/;
    matches=text_string.match(pattern);
    if(matches != null)
      return replace_in_string(matches[1], replace_hash);
    else
      return "not found";
  }
}

Use it in your HTML code as follows:

<script language="JavaScript" type="text/javascript">
  document.write(format_number_choice("[0] No apple |[1] One Apple |[2] Two Apples |[else] Many Apples", {'Apple' : 'fruit'}, 0))
  document.write(format_number_choice("[0] No apple |[1] One Apple |[2] Two Apples |[else] Many Apples", [], 1))
  document.write(format_number_choice("[0] No apple |[1] One Apple |[2] Two Apples |[else] Many Apples", [], 2))
  document.write(format_number_choice("[0] No apple |[1] One Apple |[2] Two Apples |[else] Many Apples", [], 3))
</script>

This will output:

No fruit
One Apple
Two Apples
Many Apples

Now, just use enclose the first argument with the __() helper, and you have an internationalized format_number_choice() on the client side.