mark_unknown doesn't work

Hi,
when translating, setting `mark_unknown` to False, does not impact the translation at all, thus always placing a "*" in front of unknown and "@", "#" and "/" in front of errors.

Furthermore, in the translate function in `__init__.py` it seem that the mark_unknown argument does not do anything; it is not invoked or used anywhere.

Any idea how to fix this?

Thanks in advance,
Dimitar