Before coming here, I had no idea that unless the rule is too basic, English Grammar is changeable, in fact, conventional grammar can be disobeyed sometimes. Although I don't have the links right now, I have seen reputed users here argued that Grammar does not speak the last sentence when we are forming a sentence. Rather I extracted the summary as Grammar should follow how people use them in their day-to-day life. As I am not a native English speaker, I thought maybe I am not up-to-date with this kind of changes. So it is worth asking here. By the way, the rules, users tend to avoid are medium level to high level rules, which are definitely hard to be grasped by a non-native speaker. Often answerers cite how this particular type of things are said in US, UK or other native English speaking countries although they are not 100% Grammatical and the poster admits it. But as it is a learners site, should not we at first hand refer them to the most Grammatical constructs? I want to know what community thinks here? Should Grammar follow conversational English when the rule is not too basic?
I think we should prefer Standard English unless it's clear from the question that the asker is interested in a non-standard construct.
I can think of two main reasons why we'd want to describe non-standard English:
ELLs need to understand many non-standard constructs, even if they choose not to make use of them themselves; and
Speaking perfect Standard English all the time can seem a bit haughty or highfalutin. Sometimes breaking the rules is more friendly or conversational.
I'm mostly convinced by reason 1, and not so much by reason 2. After all, a construct can be both informal and standard, so even if a question asks about an informal situation, I think we should give preference to standard constructs.
Still, I see nothing wrong with describing real-world usage, so long as we let readers know when something is non-standard.
as a learner’s site, should not we at first hand refer them to the most Grammatical constructs?
That depends on the question. As a general rule, I don't think so. As a learner's site, we should give answers that tell the whole story: what's rude, what's acceptable, what's common, what's appropriate for formal writing, and, yes, what's grammatical. But I see no reason why grammaticality should take precedence by default.
For example, if someone were to ask:
What's a friendly way to say goodbye to someone when they are going on a long trip?
why would we care about the "most grammatical" way to say bon voyage?
I think you'll find that the very people who write their answers, and explain that an expression is acceptable, despite it being non-standard, colloquial or slang etc... are precisely those whose writing is almost flawless from a grammatical viewpoint. Which could appear to be hypocritical.
The language experts, especially on EL&U, have such an enviable command of the written and spoken language (although I cannot be certain of the second, but more on that later) that apart from the odd typo here and there, whenever I read their answers I cannot help but say: Why can't I write or express myself that way?
I want to improve my understanding and dimestichezza (the English equivalent "familiarity" doesn't quite cut it for me) with any language I might be learning. I know that many learners have an understandable fervour to want to speak English correctly. The desire to sound natural and to speak fluently, can conflict with the grammar which many have formally learnt at school and this in turn may cause frustration and disappointment within an individual learner.
Personally, I am of the opinion it is better to point out to learners of a foreign language the "standard" and so considered "correct" forms of expression; explain why it is standard, explain its structure, and give further examples of its usage. EL&U and ELL both do that. Before you can "break" the rules (as a learner) you need to know what they are. And here is an observation I have made from life. The more you learn, the more you read, and the more you speak with native speakers, especially schooled ones (I won't apologize for sounding like a snob), the higher your standard of English becomes. And the more you, the learner, care about how you sound and write.
And here, I would like to make my final point, which learners tend to ignore or have rarely been exposed to. How people express their ideas on paper and how they speak everyday can differ widely according to the situation. Learners need to be aware that native speakers, in any country in the world, consciously or unconsciously use "non-standard" forms of expressions especially when speaking. It's faster, more friendly, you can adjust your tone and register, and immediately repeat yourself several times without sounding like a "ninny".
I think it depends on the situation in which the language in question is to be used. For example, if its a high school or college student, or for a business or professional environment, then structure, vocabulary and proper grammar are important.
However, if someone wants to know the vocabulary necessary to order a meal or shop in a store (OK probably not great examples), then common vocabulary and basic structure that is understandable is OK. It probably won't matter much if you say gave vs. have given, or if the tenses of two clauses match, I think the message will still get across. (Maybe this is an oversimplification, but the idea is not to make it more complex than necessary.)
As for questions asked on ELL, sometimes from the context you can tell the setting. But it never hurts to include in the question some context related to the environment where the question examples occur.
If a simple phrase to communicate something properly is sufficient, then its unnecessary to make it more difficult than that.
The more complex the structure, or higher the word count, the more difficult it will be to understand correctly. It depends whether you need such complexity or not.
Regarding vocabulary and usage, localization is important, especially for day-to-day spoken usage. I think one just has to learn what is needed.