unicode escaped string(Ex: "\ub85c") decoding example. useful for traditional java message bundle property files.

unicode-escaped-decode.php

<?php

/*
spring bean configuration needed p:defaultEncoding="UTF-8"

	<bean id="messageSource" class="org.springframework.context.support.ReloadableResourceBundleMessageSource"
		p:cacheSeconds="5"
		p:defaultEncoding="UTF-8"
		p:basenames="/WEB-INF/message/" />
*/

/**
 * decode unicode escapse string to utf8 (Ex: "\ub85c")
 * @see https://stackoverflow.com/questions/2934563/how-to-decode-unicode-escape-sequences-like-u00ed-to-proper-utf-8-encoded-cha
 */
function toUtf8($unicode_escaped_str) {
    $str = preg_replace_callback('/\\\\u([0-9a-fA-F]{4})/', function ($match) {
            return mb_convert_encoding(pack('H*', $match[1]), 'UTF-8', 'UCS-2BE');
    }, $unicode_escaped_str);

    return $str;
}

function propertyFileDecode($propFile)
{
    // backup file
    $origFile =  $propFile . ".orig";
    if (!file_exists($origFile)) {
        copy($propFile, $origFile);
    }

    $workFile =  $propFile . ".work";

    copy($propFile, $workFile);
    
    $sh = fopen($workFile, "r"); 
    $oh = fopen($propFile , "w"); 
    
    while ( !feof($sh)) {
        $line = fgets($sh);
        $line = toUtf8($line);
        fwrite($oh, $line);
    }

    fclose($sh);
    fclose($oh);

    delete($workFile);
}

$rii = new RecursiveIteratorIterator(new RecursiveDirectoryIterator('src'));

$files = [];

foreach ($rii as $file) {

    if ($file->isDir()){ 
        continue;
    }
    
    $fn = $file->getPathname();
    if (fnmatch("*.properties", $fn)) {
        $files[] = $fn;
    }

}

foreach ($files as $f) {
    print "Convert file $f \n";
    propertyFileDecode($f);
}