My guess: Czech. :)

Native English speakers living for a decade or more in the Czech Republic (and picking up Czech in the process) may experience "retroactive article confusion", they may start to drop articles while speaking their mother tongue English.

My guess is something Slavic (since Slavic languages lack articles apart from Sorbian). I could be wrong. I don't think Finno-Ugric languages have them either. That's just Europe, there are plenty of such examples elsewhere — Japanese has tonnes of suffixes but no direct equivalent to this?

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