API response breaking special characters in French

Hi all,

I've encountered a very odd issue after translating a CI 4.1.3 app to French in which XHR response is received with messed up characters by the browser.

<?php
$id = 'doesntMatter';
$message = 'L\'enregistrement de Ville a été supprimé avec succès.';
$locale = $this->request->getLocale();
log_message('debug', 'locale: ', $locale); // it is 'fr' alright
?>

When using:

<?php
return redirect()->to(route_to('cities'))->with('success', $message);
?>

Browser outputs:
L'enregistrement de Ville a été supprimé avec succès.

But when using it in a RESTful controller as an API reponse:
<?php
$reponse = $this->respondDeleted(['id' => $id], $message);
log_message('debug', var_export($response, true));
return $response;
?>

In the log, $message is dumped correctly, but the browser outputs:

L'enregistrement de Ville a été supprimé avec succès.

I'm 100% positive that all PHP files and request headers are UTF-8. (Occurred with both Chrome and Safari)

This looks like a framework bug, but I will appreciate any workaround suggestions to fix it before a possible bugfix.

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