#!/usr/bin/env php

<?php

    $str = 'Вот string на двух languages';

    preg_match_all('/[a-zA-Z]+/', $str, $matches_en);
    preg_match_all('/[а-яА-ЯЁё]+/u', $str, $matches_ru);

    var_dump ($matches_en, $matches_ru);

array(1) {
  [0]=>
  array(2) {
    [0]=>
    string(6) "string"
    [1]=>
    string(9) "languages"
  }
}
array(1) {
  [0]=>
  array(3) {
    [0]=>
    string(6) "Вот"
    [1]=>
    string(4) "на"
    [2]=>
    string(8) "двух"
  }
}