When can you tell whether one has mastered a foreign language?
Does mastering a foreign language mean you speak it like a native speaker, without no accent coming from your mother tongue(s)?

When you hear so-and-so can speak the *blank* language." what level of fluency is generally expected?

If someone is able to articulate him/herself on a very complex topic and argue with an equally knowlegeable native speaker, would you say he/she has mastered the language?

It seems that for some languages learners, "mastering" the language(s) they are learning is their ultimate goal, but how do they define a "mastery" of language? Since there is no objective perfection in this world, why do some people use the word, master???

Please share your opinions on this. Thanks!!

Question

When can you tell whether one has mastered a foreign language?
Does mastering a foreign language mean you speak it like a native speaker, without no accent coming from your mother tongue(s)?

When you hear so-and-so can speak the *blank* language." what level of fluency is generally expected?

If someone is able to articulate him/herself on a very complex topic and argue with an equally knowlegeable native speaker, would you say he/she has mastered the language?

It seems that for some languages learners, "mastering" the language(s) they are learning is their ultimate goal, but how do they define a "mastery" of language? Since there is no objective perfection in this world, why do some people use the word, master???

Please share your opinions on this. Thanks!!

Answer

There is no objective perfection in this world?!  You are getting rather philosophical in asking your question about mastery of a language.  :)

From personal experience, I would say that mastery of language comes from being able to think in another language without using your language as a crutch.  That is, you know you have mastered a language when you can intuit what you want to say and are able to say it without the help of a translator.

I do not think this necessarily requires that you are able to articulate yourself well about a complex topic.  I know people who are not able to do so in English even though it is their native language, much less would I expect them to in another language.

Answer

Because it is obvious to both speaker and learner when you have reached the point where you can say you have mastered the language. 
I can speak both Japanese and Chinese, but am nowhere near mastery.
On the other hand I have mastered German, even though I still make mistakes.
I assure you, I know the difference.

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