<?php
$re = iconv("utf-8", "cp1251", "/-[а-я]+=/");
$rei = iconv("utf-8", "cp1251", "/-[а-я]+=/i");
$RE = iconv("utf-8", "cp1251", "/-[а-яА-Я]+=/");
$str = iconv("utf-8", "cp1251", "-Превед=");
var_dump(mb_convert_encoding("-Превед=", "cp1251", "utf-8"));
var_dump($str);
var_dump(mb_detect_encoding($str, "auto", true));
var_dump($re, preg_match($re, $str));
var_dump($rei, preg_match($rei, $str));
var_dump($RE, preg_match($RE, $str));
preferences:
45.68 ms | 402 KiB | 5 Q