@Rus: I would need more information, but I suspect you might have an outdated python-polib installed on your system. Pushed a possible workaround, let me know if it still fails.
Another possible solution in that case would be to change python -m venv env --system-site-packages
to just python -m venv env
to avoid using packages already installed system-wide.
Pinned Comments
itsnotme commented on 2019-07-21 13:08 (UTC)
If anyone is wondering why the source has changed, Dupeguru's website says the maintainer has changed. And so the link https://www.hardcoded.net/dupeguru/ leads us to https://dupeguru.voltaicideas.net/ which in turn has a link to https://github.com/arsenetar/dupeguru/ which is the GitHub repo the sources are downloaded from. So the source change is legitimate.