A more complete and working version of mb_sprintf and mb_vsprintf. It should work with any "ASCII preserving" encoding such as UTF-8 and all the ISO-8859 charsets. It handles sign, padding, alignment, width and precision. Argument swapping is not handled.
<?php
if (!function_exists('mb_sprintf')) {
 function mb_sprintf($format) {
 $argv = func_get_args() ;
 array_shift($argv) ;
 return mb_vsprintf($format, $argv) ;
 }
}
if (!function_exists('mb_vsprintf')) {
 /**
 * Works with all encodings in format and arguments.
 * Supported: Sign, padding, alignment, width and precision.
 * Not supported: Argument swapping.
 */
 function mb_vsprintf($format, $argv, $encoding=null) {
 if (is_null($encoding))
 $encoding = mb_internal_encoding();
 // Use UTF-8 in the format so we can use the u flag in preg_split
 $format = mb_convert_encoding($format, 'UTF-8', $encoding);
 $newformat = ""; // build a new format in UTF-8
 $newargv = array(); // unhandled args in unchanged encoding
 while ($format !== "") {
 
 // Split the format in two parts: $pre and $post by the first %-directive
 // We get also the matched groups
 list ($pre, $sign, $filler, $align, $size, $precision, $type, $post) =
 preg_split("!\%(\+?)('.|[0 ]|)(-?)([1-9][0-9]*|)(\.[1-9][0-9]*|)([%a-zA-Z])!u",
 $format, 2, PREG_SPLIT_DELIM_CAPTURE) ;
 $newformat .= mb_convert_encoding($pre, $encoding, 'UTF-8');
 
 if ($type == '') {
 // didn't match. do nothing. this is the last iteration.
 }
 elseif ($type == '%') {
 // an escaped %
 $newformat .= '%%';
 }
 elseif ($type == 's') {
 $arg = array_shift($argv);
 $arg = mb_convert_encoding($arg, 'UTF-8', $encoding);
 $padding_pre = '';
 $padding_post = '';
 
 // truncate $arg
 if ($precision !== '') {
 $precision = intval(substr($precision,1));
 if ($precision > 0 && mb_strlen($arg,$encoding) > $precision)
 $arg = mb_substr($precision,0,$precision,$encoding);
 }
 
 // define padding
 if ($size > 0) {
 $arglen = mb_strlen($arg, $encoding);
 if ($arglen < $size) {
 if($filler==='')
 $filler = ' ';
 if ($align == '-')
 $padding_post = str_repeat($filler, $size - $arglen);
 else
 $padding_pre = str_repeat($filler, $size - $arglen);
 }
 }
 
 // escape % and pass it forward
 $newformat .= $padding_pre . str_replace('%', '%%', $arg) . $padding_post;
 }
 else {
 // another type, pass forward
 $newformat .= "%$sign$filler$align$size$precision$type";
 $newargv[] = array_shift($argv);
 }
 $format = strval($post);
 }
 // Convert new format back from UTF-8 to the original encoding
 $newformat = mb_convert_encoding($newformat, $encoding, 'UTF-8');
 return vsprintf($newformat, $newargv);
 }
}
?>