How rude is it to speak to a Japanese stranger informally instead of using the polite form?


Are there any native Japanese here that could tell me how rude it is to speak
informally to Japanese people I have never met instead of using the polite
form? I'm assuming it's more rude the older the stranger is than me?

This came up recently when I was at a conference and ran into a couple of
Japanese guys about my age (maybe in their 30's) and they seemed to speak less
English than I was able to speak Japanese, so we mostly spoke in Japanese.
It's been a few years since I've studied Japanese and I've forgotten quite a
bit, but I used to have Japanese friends in college and became more
comfortable using the non-polite form so that's what I seem to remember the
best. But I did not want to offend these guys so I found myself pausing and
stuttering trying to quickly remember how to conjugate things politely and the
conversation seemed pretty rough and even then I would pop out an informal
verb here and there. If I had spoken informally I think it would have been
much smoother and in my mind that would have been better for all of us.

So until I get better, wouldn't it be better to say something impolitely than
to not say anything at all? Would strangers care that much or would they at
least be appreciative that you are trying to speak even if it's impolite?

Examples:

「どこからきた？」instead of「どこから来ましたか」

「これ何？」instead of「これはなんですか」




Language is about communication, first and foremost, but whereas in many
languages (such as English) the focus is on getting the information in itself
across as smoothly as possible, other languages (such as Japanese, German or
the romance languages) require the encoding of social relationships along with
the information. Why this should be so isn't necessarily important; but it
_is_ so.

In general, failure to include this information hovers somewhere between
"acceptable given that you are a foreigner" and "quite rude indeed"; depending
on the level of intimacy in the conversation.

In Japanese, these social requirements are far more formal than in most
languages, but because of the overall structure of the language, there exists
an "out". (These two things are probably related.)

This is not a permanent solution; the permanent solution is to learn how to
conjugate verbs. But as a stop-gap measure while you bone up on your formal
forms, attaching です (or でございます) to the end of your sentences can help
lubricate social interactions. While it's not by any stretch of the
imagination the _right_ way to form appropriately formal sentences, it shows
that you are aware of the appropriate level of formality, even if you don't
have the means to express it correctly.

**Edit:**

With regards to specific examples: I can't speak to 「どこから来たか？」, but in
general, direct translations will lead you astray. What verbs mean in
different tenses vary from language to language; and what sentences mean
idiomatically vary from language to language. As an example, if someone seems
like they have a headache, you might be tempted to ask if their head is okay;
「頭大丈夫か？」. Unfortunately, when translated directly, this doesn't come across so
much as "I notice that you appear to be having a headache, is there anything I
can do to help?" as it comes across as "Are you nuts?"

