"?" in archive list (foreign character)

Have you got the Locale set in System Settings under Lexicon and Language? Try pl_PL as the value. If I do this it renders all my dates in Polish.

no change:/ still "?" in dates

Go into MODX System options, find variable "locale" and try these values
pl
pl_PL
pl_PL.UTF-8
pl_PL.utf8
in every case: clear cache then do full refresh in your browser. It may not work, cause I suspect that Archivist caches months names in some way and clearing MODX cache doesn't affect it. I've looked thru it's code but still have no idea how it works.

pl_PL.UTF-8 works !
but still I would like to know "why"

MODX uses PHP's strftime to get date and this function uses encoding set in 'locale' system variablee. Standard polish encoding set by locale=pl_PL is ISO 8859-2 but your page is encoded in UTF-8. That's why it differs from other strings in MODX (encoded by database).
As a side note, UTF-8 doesn't work when using webserver under Windows, so don't be surprised when you start using PHP on local computer.

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