Make SEO friendly URI. Includes cyrillic subset.

make_slug.php

<?php
/**
	 * Convert a phrase to a SEO friendly uri (slug).
	 *
	 * @param   string   $title       Phrase to convert
	 * @param   string   $separator   Word separator
	 * @param   boolean  $ascii_only  Transliterate to ASCII?
	 * @return  string
	 */
function make_slug($title, $separator = '-', $ascii_only = true) {
	if ($ascii_only === TRUE) {
		// Transliterate non-ASCII characters
		$title = transliterate_to_ascii($title);

		// Remove all characters that are not the separator, a-z, 0-9, or whitespace
		$title = preg_replace('![^' . preg_quote($separator) . 'a-z0-9\s]+!', '', strtolower($title));
	} else {
		// Remove all characters that are not the separator, letters, numbers, or whitespace
		$title = preg_replace('![^' . preg_quote($separator) . '\pL\pN\s]+!u', '', mb_strtolower($title));
	}

	// Replace all separator characters and whitespace by a single separator
	$title = preg_replace('![' . preg_quote($separator) . '\s]+!u', $separator, $title);

	// Trim separators from the beginning and end
	return trim($title, $separator);
}

/**
	 * @param   string   string to transliterate
	 * @param   integer  -1 lowercase only, +1 uppercase only, 0 both cases
	 * @return  string
	 */
function transliterate_to_ascii($str, $case = 0) {
	static $UTF8_LOWER_ACCENTS = NULL;
	static $UTF8_UPPER_ACCENTS = NULL;

	if ($case <= 0) {
		if ($UTF8_LOWER_ACCENTS === NULL) {
			$UTF8_LOWER_ACCENTS = array(
				'à' => 'a', 'ô' => 'o', 'ď' => 'd', 'ḟ' => 'f', 'ë' => 'e', 'š' => 's', 'ơ' => 'o',
				'ß' => 'ss', 'ă' => 'a', 'ř' => 'r', 'ț' => 't', 'ň' => 'n', 'ā' => 'a', 'ķ' => 'k',
				'ŝ' => 's', 'ỳ' => 'y', 'ņ' => 'n', 'ĺ' => 'l', 'ħ' => 'h', 'ṗ' => 'p', 'ó' => 'o',
				'ú' => 'u', 'ě' => 'e', 'é' => 'e', 'ç' => 'c', 'ẁ' => 'w', 'ċ' => 'c', 'õ' => 'o',
				'ṡ' => 's', 'ø' => 'o', 'ģ' => 'g', 'ŧ' => 't', 'ș' => 's', 'ė' => 'e', 'ĉ' => 'c',
				'ś' => 's', 'î' => 'i', 'ű' => 'u', 'ć' => 'c', 'ę' => 'e', 'ŵ' => 'w', 'ṫ' => 't',
				'ū' => 'u', 'č' => 'c', 'ö' => 'o', 'è' => 'e', 'ŷ' => 'y', 'ą' => 'a', 'ł' => 'l',
				'ų' => 'u', 'ů' => 'u', 'ş' => 's', 'ğ' => 'g', 'ļ' => 'l', 'ƒ' => 'f', 'ž' => 'z',
				'ẃ' => 'w', 'ḃ' => 'b', 'å' => 'a', 'ì' => 'i', 'ï' => 'i', 'ḋ' => 'd', 'ť' => 't',
				'ŗ' => 'r', 'ä' => 'a', 'í' => 'i', 'ŕ' => 'r', 'ê' => 'e', 'ü' => 'u', 'ò' => 'o',
				'ē' => 'e', 'ñ' => 'n', 'ń' => 'n', 'ĥ' => 'h', 'ĝ' => 'g', 'đ' => 'd', 'ĵ' => 'j',
				'ÿ' => 'y', 'ũ' => 'u', 'ŭ' => 'u', 'ư' => 'u', 'ţ' => 't', 'ý' => 'y', 'ő' => 'o',
				'â' => 'a', 'ľ' => 'l', 'ẅ' => 'w', 'ż' => 'z', 'ī' => 'i', 'ã' => 'a', 'ġ' => 'g',
				'ṁ' => 'm', 'ō' => 'o', 'ĩ' => 'i', 'ù' => 'u', 'į' => 'i', 'ź' => 'z', 'á' => 'a',
				'û' => 'u', 'þ' => 'th', 'ð' => 'dh', 'æ' => 'ae', 'µ' => 'u', 'ĕ' => 'e', 'ı' => 'i',
				'а' => 'a', 'б' => 'b', 'в' => 'v', 'г' => 'g', 'д' => 'd', 'е' => 'e', 'ё' => 'e',
				'ж' => 'zh', 'з' => 'z', 'и' => 'i', 'й' => 'y', 'к' => 'k', 'л' => 'l', 'м' => 'm',
				'н' => 'n', 'о' => 'o', 'п' => 'p', 'р' => 'r', 'с' => 's', 'т' => 't', 'у' => 'u',
				'ф' => 'f', 'х' => 'kh', 'ц' => 'ts', 'ч' => 'ch', 'ш' => 'sh', 'щ' => 'sch', 'ъ' => '',
				'ы' => 'y', 'ь' => '', 'э' => 'e', 'ю' => 'yu', 'я' => 'ya',
			);
		}

		$str = str_replace(
			array_keys($UTF8_LOWER_ACCENTS), array_values($UTF8_LOWER_ACCENTS), $str
		);
	}

	if ($case >= 0) {
		if ($UTF8_UPPER_ACCENTS === NULL) {
			$UTF8_UPPER_ACCENTS = array(
				'À' => 'A', 'Ô' => 'O', 'Ď' => 'D', 'Ḟ' => 'F', 'Ë' => 'E', 'Š' => 'S', 'Ơ' => 'O',
				'Ă' => 'A', 'Ř' => 'R', 'Ț' => 'T', 'Ň' => 'N', 'Ā' => 'A', 'Ķ' => 'K', 'Ĕ' => 'E',
				'Ŝ' => 'S', 'Ỳ' => 'Y', 'Ņ' => 'N', 'Ĺ' => 'L', 'Ħ' => 'H', 'Ṗ' => 'P', 'Ó' => 'O',
				'Ú' => 'U', 'Ě' => 'E', 'É' => 'E', 'Ç' => 'C', 'Ẁ' => 'W', 'Ċ' => 'C', 'Õ' => 'O',
				'Ṡ' => 'S', 'Ø' => 'O', 'Ģ' => 'G', 'Ŧ' => 'T', 'Ș' => 'S', 'Ė' => 'E', 'Ĉ' => 'C',
				'Ś' => 'S', 'Î' => 'I', 'Ű' => 'U', 'Ć' => 'C', 'Ę' => 'E', 'Ŵ' => 'W', 'Ṫ' => 'T',
				'Ū' => 'U', 'Č' => 'C', 'Ö' => 'O', 'È' => 'E', 'Ŷ' => 'Y', 'Ą' => 'A', 'Ł' => 'L',
				'Ų' => 'U', 'Ů' => 'U', 'Ş' => 'S', 'Ğ' => 'G', 'Ļ' => 'L', 'Ƒ' => 'F', 'Ž' => 'Z',
				'Ẃ' => 'W', 'Ḃ' => 'B', 'Å' => 'A', 'Ì' => 'I', 'Ï' => 'I', 'Ḋ' => 'D', 'Ť' => 'T',
				'Ŗ' => 'R', 'Ä' => 'A', 'Í' => 'I', 'Ŕ' => 'R', 'Ê' => 'E', 'Ü' => 'U', 'Ò' => 'O',
				'Ē' => 'E', 'Ñ' => 'N', 'Ń' => 'N', 'Ĥ' => 'H', 'Ĝ' => 'G', 'Đ' => 'D', 'Ĵ' => 'J',
				'Ÿ' => 'Y', 'Ũ' => 'U', 'Ŭ' => 'U', 'Ư' => 'U', 'Ţ' => 'T', 'Ý' => 'Y', 'Ő' => 'O',
				'Â' => 'A', 'Ľ' => 'L', 'Ẅ' => 'W', 'Ż' => 'Z', 'Ī' => 'I', 'Ã' => 'A', 'Ġ' => 'G',
				'Ṁ' => 'M', 'Ō' => 'O', 'Ĩ' => 'I', 'Ù' => 'U', 'Į' => 'I', 'Ź' => 'Z', 'Á' => 'A',
				'Û' => 'U', 'Þ' => 'Th', 'Ð' => 'Dh', 'Æ' => 'Ae', 'İ' => 'I',
				'А' => 'A', 'Б' => 'B', 'В' => 'V', 'Г' => 'G', 'Д' => 'D', 'Е' => 'E', 'Ё' => 'E',
				'Ж' => 'ZH', 'З' => 'Z', 'И' => 'I', 'Й' => 'Y', 'К' => 'K', 'Л' => 'L', 'М' => 'M',
				'Н' => 'N', 'О' => 'O', 'П' => 'P', 'Р' => 'R', 'С' => 'S', 'Т' => 'T', 'У' => 'U',
				'Ф' => 'F', 'Х' => 'KH', 'Ц' => 'TS', 'Ч' => 'CH', 'Ш' => 'SH', 'Щ' => 'SCH', 'Ъ' => '',
				'Ы' => 'Y', 'Ь' => '', 'Э' => 'E', 'Ю' => 'YU', 'Я' => 'YA',
			);
		}

		$str = str_replace(
			array_keys($UTF8_UPPER_ACCENTS), array_values($UTF8_UPPER_ACCENTS), $str
		);
	}

	return $str;
}