$re = '/(numberPinyin":\s*".*)(v)(.*)"/m';
$str = '[\'{"russian": "женщина", "english": "woman, v","numberPinyin": "nv3","typeOfChar":"character","typeOfTranslating":"original"}\',
\'{"chinese": "弯竖左钩", "russian": "вогнутая с крюком влево", "english": "concave with left hook","numberPinyin": "eav","typeOfChar":"stroke","typeOfTranslating":"byStrokes"}\',
\'{"chinese": "弯竖右钩", "russian": "вогнутая с крюком вправо", "english": "concave with right hook","numberPinyin": "vm2","typeOfChar":"stroke","typeOfTranslating":"byStrokes"}\']';
$subst = "\1ü\3";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php