def METHOD_NAME(data_folder):
    """
    Check if the data folder actually contains the CommonLanguage dataset.
    If not, raises an error.
    Returns
    -------
    None
    Raises
    ------
    FileNotFoundError
        If data folder doesn't contain at least two languages.
    """
    # Checking if at least two languages are present in the data
    if len(set(os.listdir(data_folder)) & set(LANGUAGES)) < 2:
        err_msg = f"{data_folder} must have at least two languages from CommonLanguage in it."
        raise FileNotFoundError(err_msg)