<?php
$correspondances = array(
  "mot1" => "https://www.lien1.com",
  "mot2" => "https://www.lien2.com",
);

function linkifyText($text, $correspondances) {
  $pattern = "/#(\w+)#/";
  $result = preg_replace_callback($pattern, function($matches) use ($correspondances) {
    $word = $matches[1];
    if (array_key_exists($word, $correspondances)) {
      $link = '<a href="' . $correspondances[$word] . '">' . $word . '</a>';
      return $link;
    } else {
      return $word;
    }
  }, $text);
  return $result;
}

$texte = "Voici un exemple de #mot1# et de #mot2#.";
$texteLinkifie = linkifyText($texte, $correspondances);
echo $texteLinkifie;
?&gt;