What does this do?

@Anahkiasen This replaces "toAscii" methods by the PHP transliterator function.
See #311.

Yes, you should provide an alternative implementation without intl, similar to what the toAscii() method did in the past. Something like:

private static function transliterate($string)
{
    if (function_exists('transliterator_transliterate')) {
        // fine, use intl
        // ...
    } else {
        // use the old special char replacement technique
        // with a unique replacement matrix for all locales
    }

    return $string;
}

That way, you can remove the part in README.md about intl being a requirement.

Also, transliterateEmail() shouldn't do an if, since the translitterate() method will always return the translitterated string.

Lastly, tests fail.

Despite the use of my best toAscii method I'm not able to make the tests go green. There are too many char to normalize.
For the record I've found some interesting things like this intl implementation by symfony
https://github.com/symfony/Intl
I don't know if we can use it though.
BTW, This site inspired my solution for this problem http://camendesign.com/code/transliteration

Superseded by #490