Outputting other languages to Cloud Pub/Sub topics

I'm using Google Cloud Functions in conjunction with their Vision API and Translate API to extract text from images and then translate the extracted text into various languages. The output is passed to a Pub/Sub topic and then stored in a Cloud Storage bucket. All the components appear to be working fine, except my output is not properly encoded for the language, so I'm getting strings like "Pâté Oeufs Mimosa" rather than "Pâté – Oeufs Mimosa".

Here's the relevant code I'm using:

# [START functions_ocr_detect]
def detect_text(bucket, filename):
    print('Looking for text in image {}'.format(filename))

    futures = []

    text_detection_response = vision_client.text_detection({
        'source': {'image_uri': 'gs://{}/{}'.format(bucket, filename)}
    })
    annotations = text_detection_response.text_annotations
    if len(annotations) > 0:
        text = annotations[0].description
    else:
        text = ''
    print('Extracted text {} from image ({} chars).'.format(text, len(text)))

    detect_language_response = translate_client.detect_language(text)
    src_lang = detect_language_response['language']
    print('Detected language {} for text {}.'.format(src_lang, text))

    # Submit a message to the bus for each target language
    for target_lang in TO_LANG:
        topic_name = TRANSLATE_TOPIC
        if src_lang == target_lang or src_lang == 'und':
            topic_name = RESULT_TOPIC
        message = {
            'text': text,
            'filename': filename,
            'lang': target_lang,
            'src_lang': src_lang
        }
        message_data = json.dumps(message).encode('utf-8')
        topic_path = publisher.topic_path(project_id, topic_name)
        future = publisher.publish(topic_path, data=message_data)
        futures.append(future)
    for future in futures:
        future.result()
# [END functions_ocr_detect]


# [START message_validatation_helper]
def validate_message(message, param):
    var = message.get(param)
    if not var:
        raise ValueError('{} is not provided. Make sure you have \
                          property {} in the request'.format(param, param))
    return var
# [END message_validatation_helper]


# [START functions_ocr_process]
def process_image(file, context):
    """Cloud Function triggered by Cloud Storage when a file is changed.
    Args:
        file (dict): Metadata of the changed file, provided by the triggering
                                 Cloud Storage event.
        context (google.cloud.functions.Context): Metadata of triggering event.
    Returns:
        None; the output is written to stdout and Stackdriver Logging
    """
    bucket = validate_message(file, 'bucket')
    name = validate_message(file, 'name')

    detect_text(bucket, name)

    print('File {} processed.'.format(file['name']))
# [END functions_ocr_process]


# [START functions_ocr_translate]
def translate_text(event, context):
    if event.get('data'):
        message_data = base64.b64decode(event['data']).decode('utf-8')
        message = json.loads(message_data)
    else:
        raise ValueError('Data sector is missing in the Pub/Sub message.')

    text = validate_message(message, 'text')
    filename = validate_message(message, 'filename')
    target_lang = validate_message(message, 'lang')
    src_lang = validate_message(message, 'src_lang')

    print('Translating text into {}.'.format(target_lang))
    translated_text = translate_client.translate(text,
                                                 target_language=target_lang,
                                                 source_language=src_lang)
    topic_name = RESULT_TOPIC']
    message = {
        'text': translated_text['translatedText'],
        'filename': filename,
        'lang': target_lang,
    }
    message_data = json.dumps(message).encode('utf-8')
    topic_path = publisher.topic_path(project_id, topic_name)
    future = publisher.publish(topic_path, data=message_data)
    future.result()
# [END functions_ocr_translate]


# [START functions_ocr_save]
def save_result(event, context):
    if event.get('data'):
        message_data = base64.b64decode(event['data']).decode('utf-8')
        message = json.loads(message_data)
    else:
        raise ValueError('Data sector is missing in the Pub/Sub message.')

    text = validate_message(message, 'text')
    filename = validate_message(message, 'filename')
    lang = validate_message(message, 'lang')

    print('Received request to save file {}.'.format(filename))

    bucket_name = RESULT_BUCKET
    result_filename = '{}_{}.txt'.format(filename, lang)
    bucket = storage_client.get_bucket(bucket_name)
    blob = bucket.blob(result_filename)

    print('Saving result to {} in bucket {}.'.format(result_filename, bucket_name))
    blob.upload_from_string(text)

    print('File saved.')
# [END functions_ocr_save]

A blob / object features a content_encoding, content_type and content_language header... which probably should be: content_type='text/plain'; charset='utf-8', content_encoding='utf-8', content_language='fr'.