<?php
 
$latin = ['dž', 'lj', 'nj',
    'a', 'b', 'c', 'č', 'ć',
    'd', 'đ', 'e', 'f', 'g',
    'h', 'i', 'j', 'k', 'l',
    'm', 'n', 'o', 'p', 'r', 
    's', 'š', 't', 'u', 'v', 
    'z', 'ž',
    'DŽ', 'LJ', 'NJ', 'Dž', 'Lj', 'Nj',
    'A', 'B', 'C', 'Č', 'Ć',
    'D', 'Đ', 'E', 'F', 'G',
    'H', 'I', 'J', 'K', 'L',
    'M', 'N', 'O', 'P', 'R', 
    'S', 'Š', 'T', 'U', 'V', 
    'Z', 'Ž'
];
 
$cyrillic = ['џ', 'љ', 'њ',
    'a', 'б', 'ц', 'ч', 'ћ',
    'д', 'ђ', 'e', 'ф', 'г',
    'x', 'и', 'j', 'к', 'л',
    'm', 'н', 'o', 'п', 'p', 
    'c', 'ш', 'т', 'y', 'b', 
    'з', 'ж',
    'Џ', 'Љ', 'Њ', 'Џ', 'Љ', 'Њ',
    'A', 'Б', 'Ц', 'Ч', 'Ћ',
    'Д', 'Ђ', 'E', 'Ф', 'Г',
    'X', 'И', 'J', 'K', 'Л',
    'M', 'H', 'O', 'П', 'P', 
    'C', 'Ш', 'T', 'Y', 'B', 
    'З', 'Ж'
];
 
$arr = array_combine($latin, $cyrillic);
$string = 'Today is {day_name} and time is {time}';
 
echo preg_replace_callback('/\{[^}]*}(*SKIP)(*F)|./', function ($m) use ($arr) {
	  return array_key_exists($m[0], $arr) ? $arr[$m[0]] : $m[0];
	},
	$string);

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