So, I’m learning japanese as a foreign language, and by no means am fluent, but it’s also the fifth foreign language I’ve learned, and I feel like a lot of the things people are ascribing to japanese and it’s effect on their thinking and personality are more reflective of the effects of being non-fluent rather than necessarily the structure of the language or culture. Like I’m way less sarcastic in japanese, I joke around less in japanese, but both sarcasm and jokes require a level of nuance and a sense of security that your audience understands what you mean that you just can’t have in a language you don’t have a solid grasp on. I had the same thing happen to me when I was at the intermediate level in my hebrew studies– the cognitive load of expressing myself sincerely, even though I didn’t notice it because I was starting to feel some fluency, was still so high that sarcasm or word play was outside the realm of conscious thought.
Also, with the politeness thing, I used to think it was japanese specific, but I’m realizing through teaching english that we have literally the same sets of conventions, they’re just more complicated. While japanese has honorofics like さん, さま, くん, ちゃん, どの and 先生, English will literally conjugate people’s names according to how well we know them and whether or not they are at the same social level, above, or below, and in what circumstances. For example, pretend there’s a woman named Kristine Smith. You can call her Kristine Smith at a role call, Ms. Smith if he’s your boss, Kristine if you’re her boss, Kris if you’re her friend, Krissy if you’re her elder sibling or parent, and K-dawg if you’re on her basketball team. To say nothing of the various relationships you assume/reinforce by calling her “miss,” “ma’m” “bae” “toots” “girlfriend” “lady” or “officer.”
One thing that I will say about japanese as being different from English is the tendency to embed information in sentences by nominalizing them as aspects of a subject, saying things that if directly translated will be “I like that getting-things-done-despite-feeling-guilty part of you” instead of “I like how you get things done even if you feel guilty.” It’s a small difference, but it adds up for me to feel like japanese folks are more willing to define parts of themselves and others in whatever context, where as in English our capabilities or choices are often separate from our idea of ourselves, and you can be pretty rude or pushy (or straight up abusive) if you try to tell somebody who they are to their face, even if all you’re doing is naming their own behavior. I don’t think its good or bad– it feels empowering to me (like I can define myself and change my fundamental identity without it being a big deal), but I can see how it could also lead to stereotyping and stuff.