Normally I'd agree, a windows-1252 misencode should be one's default guess when mojibake is afoot. Unfortunately, the errant byte in the error is 0xb3, which is "³" in windows-1252.
If you Google, "Mikołaj",
> Mikołaj is the Polish cognate of given name Nicholas
Then Google, "windows character encoding polish"
> Windows-1250 - Wikipedia
And 0xb3 is "ł" in that encoding.¹
> Does it work if you set the environment variable PYTHONENCODING (sic) to cp1252?
I don't know if setting PYTHONIOENCODING would work here; I don't think it should affect this. Really, fixing the YAML file is the fix. (And fixing the thing that generated it.)
¹it is queries like this that really make me love the search engines of today. This would have been hell in the days of Alta Vista.
If you Google, "Mikołaj",
> Mikołaj is the Polish cognate of given name Nicholas
Then Google, "windows character encoding polish"
> Windows-1250 - Wikipedia
And 0xb3 is "ł" in that encoding.¹
> Does it work if you set the environment variable PYTHONENCODING (sic) to cp1252?
I don't know if setting PYTHONIOENCODING would work here; I don't think it should affect this. Really, fixing the YAML file is the fix. (And fixing the thing that generated it.)
¹it is queries like this that really make me love the search engines of today. This would have been hell in the days of Alta Vista.