PHP | Google Translate API doesn't translate FR text

one text

I use GoogleTranslateV2, The function works with any other language - except 'fr' (French).

Here's the function:

function translate($lang) {
    global $google_translation, $post_heading, $post_subtitle;
    //The data you want to send via POST
    $fields = [
        'q' => array($post_heading,$post_subtitle),
        'target' => $lang,
        'format' => 'text',
        'source' => 'en',
        'key' => $gtranslate_key
    ];
    //url-ify the data for the POST
    $fields_string = preg_replace('/%5B(?:[0-9]|[1-9][0-9]+)%5D=/', '=', http_build_query($fields));
    //open connection
    $ch = curl_init();
    //set the url, number of POST vars, POST data
    curl_setopt($ch,CURLOPT_URL, $google_translation);
    curl_setopt($ch,CURLOPT_POST, true);
    curl_setopt($ch,CURLOPT_POSTFIELDS, $fields_string);
    //So that curl_exec returns the contents of the cURL; rather than echoing it
    curl_setopt($ch,CURLOPT_RETURNTRANSFER, true); 
    //execute post
    $result = curl_exec($ch);
    return json_decode($result, true);
}

I tried several other languages, every other language works. When I try to translate to French, I get the response in English (not translated). I see no reason for this to happen, is there something I'm missing?

Source