<?php

$str = "<body><span class=\"TermText qWord lang-fr\">Je suis</span>";
$dom = new DOMDocument;
@$dom->loadHTML($str, LIBXML_HTML_NOIMPLIED|LIBXML_HTML_NODEFDTD);
$xp = new DOMXPath($dom);
$spans = $xp->query('//span[contains(@class,"lang-fr")]');
$arr = array();
foreach ($spans as $span) {
 array_push($arr, $span->nodeValue);
}
print_r($arr);