How to decode Unicode escape sequences like "\u00ed" to proper UTF-8 encoded characters?

Is there a function in PHP that can decode Unicode escape sequences like "\u00ed" to "í" and all other similar occurrences?

I found similar question here but is doesn't seem to work.

Try this:

$str = preg_replace_callback('/\\\\u([0-9a-fA-F]{4})/', function ($match) {
    return mb_convert_encoding(pack('H*', $match[1]), 'UTF-8', 'UCS-2BE');
}, $str);

In case it's UTF-16 based C/C++/Java/Json-style:

$str = preg_replace_callback('/\\\\u([0-9a-fA-F]{4})/', function ($match) {
    return mb_convert_encoding(pack('H*', $match[1]), 'UTF-8', 'UTF-16BE');
}, $str);

print_r(json_decode('{"t":"\u00ed"}')); // -> stdClass Object ( [t] => í )

PHP 7+

As of PHP 7, you can use the Unicode codepoint escape syntax to do this.

echo "\u{00ed}"; outputs í.