SEO friendly url converter for Vietnamese

slugify.php

<?php
    
    /**
    * Take from https://gist.github.com/alixaxel/5562152 with some edits
    */
	function slugify($string, $slug = '-', $extra = null) {
		if (strpos($string = htmlentities($string, ENT_QUOTES, 'UTF-8'), '&') !== false) {
			$string = html_entity_decode(preg_replace('~&([a-z]{1,2})(?:acute|caron|cedil|circ|grave|lig|orn|ring|slash|tilde|uml);~i', '$1', $string), ENT_QUOTES, 'UTF-8');
		}
	
		if (preg_match('~[^[:ascii:]]~', $string) > 0) {
			$latin = array(
				'a' => '~[àáảãạăằắẳẵặâầấẩẫậÀÁẢÃẠĂẰẮẲẴẶÂẦẤẨẪẬą]~iu',
				'ae' => '~[ǽǣ]~iu',
				'b' => '~[ɓ]~iu',
				'c' => '~[ćċĉč]~iu',
				'd' => '~[ďḍđɗð]~iu',
				'e' => '~[èéẻẽẹêềếểễệÈÉẺẼẸÊỀẾỂỄỆęǝəɛ]~iu',
				'g' => '~[ġĝǧğģɣ]~iu',
				'h' => '~[ĥḥħ]~iu',
				'i' => '~[ìíỉĩịÌÍỈĨỊıǐĭīįİ]~iu',
				'ij' => '~[ij]~iu',
				'j' => '~[ĵ]~iu',
				'k' => '~[ķƙĸ]~iu',
				'l' => '~[ĺļłľŀ]~iu',
				'n' => '~[ʼnń̈ňņŋ]~iu',
				'o' => '~[òóỏõọôồốổỗộơờớởỡợÒÓỎÕỌÔỒỐỔỖỘƠỜỚỞỠỢǒŏōőǫǿ]~iu',
				'r' => '~[ŕřŗ]~iu',
				's' => '~[ſśŝşșṣ]~iu',
				't' => '~[ťţṭŧ]~iu',
				'u' => '~[ùúủũụưừứửữựÙÚỦŨỤƯỪỨỬỮỰǔŭūűůų]~iu',
				'w' => '~[ẃẁŵẅƿ]~iu',
				'y' => '~[ỳýỷỹỵYỲÝỶỸỴŷȳƴ]~iu',
				'z' => '~[źżžẓ]~iu',
			);
	
			$string = preg_replace($latin, array_keys($latin), $string);
		}
	
		return strtolower(trim(preg_replace('~[^0-9a-z' . preg_quote($extra, '~') . ']++~i', $slug, $string), $slug));
	}