While writing the function to grab an 'excerpt' of text from an utterance (i.e. a chunk of text surrounding a search term), I discovered that substr_replace() is not multibyte-safe. So, if you use it with a multibyte string you might get strange results.

The excerpt() function, which is otherwise very solid and flexible, is adapted from CakePHP's text helper. I had to replace these two lines:

$excerpt = substr_replace($excerpt, $ending, 0, $phraseLen);

$excerpt = substr_replace($excerpt, $ending, -$phraseLen);

With these multibyte-safe lines:

$excerpt = mb_substr($excerpt, 0, 0) . $ending . mb_substr($excerpt, $phraseLen + 1);

$excerpt = mb_substr($excerpt, 0, -$phraseLen) . $ending . mb_substr($excerpt, $textLen);

So, in a nutshell, here's how to convert your substr_replace() call to a multibyte version:

// Original call
$string = substr_replace($text, $replacement, $start, $length);

// MB-safe call
$string = mb_substr($text, 0, $start) . $replacement . mb_substr($text, $length);