[Supperman]

Hi.
I'm a native-Japanese speaker who has been studying English for over 30 years.
I can speak English as a second language to some extent, and I can communicate with non-native English speaking people to some extent.
Yet if you are a native-English speaker, you know that I'm not a native-English speaker, because my English sentences are different from natives' English.

I think there are several levels of a language. For example;
Level one; unable to communicate, always
Level two; able to communicate, sometimes,
Level three; able to communicate, 75%,
Level four; able to communicate more than 90%, though unnatural as a native tongue
Level five;able to communicate always, almost natural
Level six; able to communicate perfectly, and identical to native-speakers

As a learner, one should have the aim to what level he should go.
AND
As a teacher, one would think what level he should request the learner to obtain.
They doesn't match from time to time, which is the cause of your trouble, right?

It depends on the situations.

If I want to take a comfortable and cheerful time with a foreign people, the Level three might be enough. My aim is not to correct his grammar, or not to improve his Japanese, but have fun with him, talking with him. In such cases, if he speaks Japanese with the level three, I would say "nihongo ga o jyouzu desune!"

If you want to improve Japanese to the level six, you should say to us about it. Then we will help you. But being-strict might be very tough thing to both of us.

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And now, suppose I would request you the proofreading of my English sentences here, what will you do?

If I say that I want to become the level six, then you have to correct most of my English, don't you?

Besides, if I say that I only want to become the level three, then you just correct a few sentences, and you would say that my English is good,
wouldn't you?

I don't think it is the nature of Japanese people, but common to all human beings.