Try following code
$textcyr="Тествам с кирилица";
$textlat="I pone dotuk raboti!";
$cyr = ['?', '?', '?', '?', 'ш', '?', 'ч', '?', 'ж', '?', '?', 'Ш', '?', 'Ч', '?', 'Ж','Ц','ц', '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', '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 = ['Lj', 'Nj', 'D?', 'd?', '?', '?', '?', '?', '?', 'lj', 'nj', '?', '?', '?', '?', '?','C','c', 'a','b','v','g','d','e','io','zh','z','i','y','k','l','m','n','o','p', 'r','s','t','u','f','h','ts','ch','sh','sht','a','i','y','e','yu','ya', 'A','B','V','G','D','E','Io','Zh','Z','I','Y','K','L','M','N','O','P', 'R','S','T','U','F','H','Ts','Ch','Sh','Sht','A','I','Y','e','Yu','Ya'
];
$textcyr = str_replace($cyr, $lat, $textcyr);
$textlat = str_replace($lat, $cyr, $textlat);
echo("$textcyr $textlat");