PHP code to convert Russian letters to Latin lower case letters

transliterate-russian-to-lower-latin.php

<?php	
function transliterate_to_lower($string)
	{
		$cyr = ['а','б','в','г','д','е','ё','ж','з','и','й','к','л','м','н','о','п', 'р','с','т','у','ф','х','ц','ч','ш','щ','ъ','ы','ь','э','ю','я'];
		$lat = ['a','b','v','g','d','e','e','zh','z','i','j','k','l','m','n','o','p','r','s','t','u','f','h','c','ch','sh','sh','','y','','e','yu','ya'];
		$strlat = str_replace($cyr, $lat, mb_strtolower($string));
		return $strlat;
	}

echo transliterate_to_lower("Привет, 1-й ёжик!");
?>

Input: Привет, 1-й ёжик!
Output: privet, 1-j ezhik!

This code may be useful to preprocess Russian strings for slugification, e.g. in URLs.
It is based on GOST R 7.0.34-2014 with the following exceptions:

• ё = e (instead of yo)
• щ = sh (instead of shh)
• ъ — omitted
• ь — omitted

It works very differently from transliterator_transliterate() where:

• ж = z
• ч = c
• ш = s
• щ = s
• Ъ = ``
• Ь = `
• ю = u
• я = a

As a result, transliterator_transliterate() does not follow the typical Russian transliteration rules.