def calculate_fee(text_len, dollar_per_currency=None):
    """
    https://cloud.google.com/translate/pricing?hl=en

    * Google charges on per character basis, even if the character is multiple bytes,
      where a character corresponds to a (code-point).
    * Google does not charge extra for language detection when you do not specify
      the source language for the translate method.
    """
    if dollar_per_currency is None:
        dollar_per_currency = 1  # dollar
    dollar = text_len / (10 ** 6) * 20
    return dollar_per_currency * dollar