The polish diminutive thing took me way longer than the case system did
Been learning Polish for around 18 months. Finished Krok po kroku 1 last winter, halfway through book 2 now, maybe 2500 words on Anki. Cases I can survive most of the time. Aspect pairs still trip me up but I can usually pick something. Reading polskieradio.pl is doable if the topic is familiar.
Started doing weekly video calls with a Polish friend around a year in. Met her on HelloTalk during a stretch when I was in "I need to actually speak this before I completely lose the ability" panic mode. She's a graphic designer in Wrocław, wanted to practice English, so we swap thirty minutes each. She's not a teacher and mostly can't explain why things sound wrong. She just goes "mmm nie" and pulls a face.
The thing that took me way too long to see was diminutives. Krok po kroku introduces them somewhere in book 1 with the standard framing, kot → kotek, dom → domek, small or cute or affectionate. I learned the suffixes, filed them in a mental drawer marked "for pets and kids," and moved on.
Then I went to Kraków for a week in spring. Ordered coffee at a place near the Rynek and said "poproszę kawę." Grammatically clean, accusative, the whole deal. Barista gave me my coffee and I noticed the person behind me ordered "poproszę kawkę." Went to a bakery the next morning and heard people asking for "chlebek" and "bułeczkę." Nobody in three days ordered anything in the plain form.
Asked my friend about it on our next call and she laughed. Said "poproszę kawę" is completely fine and polite, poproszę already does that work. But locals almost always add the diminutive on top in casual places, and skipping it makes you sound like you're reading from a phrasebook. "Kawka" or "kawusia" isn't about the coffee being small, it's about you not sounding stiff. Her grandma orders "herbatka" not "herbata," her mom emails work colleagues asking if they have "chwilkę" not "chwilę," and if you say "podaj chleb" at a family dinner instead of "podaj chlebek" you sound weirdly cold. Same content, different social temperature.
That reframing broke something open. Once I noticed it I could not stop hearing it. Waiters going "sekundkę" instead of "sekundę," my friend's mom offering "kanapeczkę" at lunch, someone on a work call asking me to wait "chwileczkę" while she pulled up a file. It's not baby talk. It's the default polite register for anything transactional or friendly, and skipping the diminutives in those contexts marks you as an outsider even when your grammar is otherwise fine.
You can also overdo it. My friend said if I ordered "kaweczkę" or "chlebeczek" I'd sound like I was being cutesy or joking, and there's a whole layer of which diminutive fits which register. Kawka and kawusia and kaweczka aren't interchangeable, they sit on different spots between neutral-polite, affectionate, and joking. Nobody really teaches you that map. You pick it up by listening to what people actually say and adjusting until nobody makes a face at you.
Kind of curious what other register stuff people ran into.