strrchr with strtr or str_replace in PHP - php

Question

I have searched a lot of sites and SO answers for replacing characters in strings, but I didn't find a solution.
I need to replace only the last used character 'é' of a string.
It should work for every string, also if the string only contains once character 'é'.
code
echo strtr (strrchr ( 'accélérer','é' ), array ('é' => 'è')); // output èrer
echo str_replace("é","è",strrchr ( 'accélérer','é' )); // output èrer
desired results
accélérer -> accélèrer
sécher-> sècher

Answer 1

Have created custom function. Might be useful:
<?php
$str = 'accélérer';
$output = replaceMultiByte($str, 'é', 'è');
echo "OUTPUT=".$output; // accélèrer
echo '<br/><br/>';
$str = 'sécher';
$output = replaceMultiByte($str, 'é', 'è');
echo "OUTPUT=".$output; // sècher
function replaceMultiByte($str, $replace, $replaceWith)
{
$exp = explode($replace, $str);
$i = 1;
$cnt = count($exp);
$format_str = '';
foreach($exp as $v)
{
if($i == 1)
{
$format_str = $v;
}
else if($i == $cnt)
{
$format_str .= $replaceWith . $v;
}
else
{
$format_str .= $replace . $v;
}
$i++;
}
return $format_str;
}
?>

Answer 2

You could do something like this:
$str = 'accélérer';
$pos = strrpos( $str, 'é' );
if( $pos !== FALSE ) $str[$pos] = 'è';

Answer 3

Mat's answer did not work on me, so I work on more and I found è is 2 btye in strlen and 1 byte in mb_strlen. So in order to work with substr_replace
$str = "accélérer";
$pos = mb_strrpos($str, "é", "UTF-8");
if ($pos !== false) {
$str = substr_replace($str, "è", $pos + 1, strlen("è") );
}
var_dump($str); // string(11) "accélèrer"