The most important rule is that other people should be able to understand you. And what they understand should ideally be the same thing you wanted to say. If people don’t understand you, then you may have crossed the “border” you mentioned.
Another “rule” is that the rules for informal language are a lot more flexible than the rules for formal language. Just as they are in German. But even for more formal English, there isn’t always 100% agreement among the experts about everything.
Michael, I met a lot of Germans in the US years before I came to Germany, years before I began teaching and years before I learned German. One thing that I enjoyed was the way my German friends spoke. I enjoyed their “original” ways of saying things.
Of course, today I know that many of these “original ways of saying things” came directly from German. But, the point is, even though many things weren’t “typical” English ways of saying things, as long as the ideas were understandable and clear, no problem! The differences just made things more interesting.
On the other hand, there can also be some things that create unwanted negative reactions or unexpected misunderstandings. For example, I remember meeting one German who often told me how “sympathetic” (mitf?hlend) his American co-workers were. Because I didn’t know how to speak German at the time, I didn’t recognize the “false friend” and didn’t understand that he wanted to tell me that he simply found his co-workers “nice” and “likeable” (sympathisch). Instead, I thought the poor guy was constantly unhappy and desperately needed his co-workers for commiseration. :shock:
Now let me ask you a question. You mentioned questions being asked in the forum where no concrete answer was given or just subjective opinions. Can you be a little more concrete than that? It’s pretty difficult to answer such a non-specific question.