Language is slippery; languages evolve; languages go off in new directions under new influences.
People can express indifference in British English by saying I couldn't care less. In America, people sometimes express the same notion with I could less less (without the negative). How flexible and creative language is!
In English, people sometimes express resignation by saying It can't be helped. If you want to cheer a friend up with this feeling, you could say It can be helped. Of course, it is much less common, but my point is that an NS's option to use language creatively is far more acceptable. When NNSs do this, it seems far less likely to be successful.
The Japanese language has a culturally marked expression for It can't be helped. They say sho ga nai This literally means there is no way to do. In contrast, when I once said sho ga aru to my friends, as a kind of language play; i.e. there IS a way to do, my friends just laughed and said that is not correct Japanese, and they wouldn't accept my intended meaning. Well, I knew it was not "correct" Japanese because I had lived here for a long time. But sometimes, advanced NNS speakers just want to be creative, and not be corrected for "mistaken" utterances.
So,
Question: what role do NNSs have to play in language variability, or even shift? I know of research on the ownership of English (e.g. http://www2.hawaii.edu/~cmhiggin/TQ_Higgins.pdf) Can you recommend similar research?
Question: What factors influence the acceptability of non-standard (creative) utterances by NNSs in the ears of NSs?
Question: How native-like do NNSs need to be to be able to create neologisms unchallenged? Is there research that describes this change longitudinally?
Question: Is there is a database, book or article detailing non-standard phrases by NSs and NNSs in English, or another language?
I have an early idea for the design of a research experiment to assess the acceptability of non-standard speech by NNSs of varying proficiency. I would be interested in doing this between English and Japanese, or other languages and Japanese, or a language pair including French.
And would anyone be interested perhaps in pursuing this as a joint research project?
David