def METHOD_NAME(filename: Text, language: Optional[Text] = "en") -> Optional["TrainingData"]:
    """Loads a single training data file from disk."""
    fformat = guess_format(filename)
    if fformat == UNK:
        raise ValueError(f"Unknown data format for file '{filename}'.")
    reader = _reader_factory(fformat)
    if reader:
        return reader.read(filename, language=language, fformat=fformat)
    else:
        return None