下面有翻译：）
I have to say, it can be tricky to evaluate your English level based on a native speaker's comment. Many people often say "your English is good" in response to a non-English speaker saying "I'm sorry for my English". Normally, if English speakers can get the main idea of one's speaking and keep the conversation going, they wouldn't want to discourage an English learner by correcting them too much.
When I am not teaching, I would say "your English is good" to mean "I can basically understand your English, and I hope you keep trying". This is more related to speaking but could also be used for writing.
When I am teaching, I don't usually give a general statement on one's English level. I would focus on correcting the students using more specific feedback. To me, the most important part of speaking English well is knowing what words mean and how to use them. One doesn't have to have a huge vocabulary or even perfect pronunciation; just knowing how to use familiar words is the most important from my perspective.
For example, I would be really impressed if I had a 5-minute conversation with a student, and did not catch any article ("the", "an", "a") mistakes.
One suggestion for people who have the opportunity to talk to a native speaker is to ask the native speaker to correct you as much as possible rather than just letting them tell you "your English is good". Only then can you improve.
I hope my answer is helpful.
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栗子的知乎答案索引：栗子树
栗子的微信公众号：E-Speller 或者 栗子英文 （只有精彩的原创）
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感谢 @SilentLeo 的中文翻译：
首先我必须说，通过一个以英语为母语者的评价来判定你的英语水平是不科学的。这是因为当一个非母语者说“对不起我英语不好”时，许多母语者通常回应“你的英语非常好”。正常情况下，如果一个英语为母语者能明白你要表达的要点并且对话可以继续，他们就不会用挑错的方式来让英语学习者沮丧。
当我尚未从事英语教学时，我会说“你的英语很好”而我此刻真正想表达的是“我基本上能听懂你的英语，希望你能继续努力”。一般这一评价针对英语口语，有时也针对英语写作。当我开始教学之后，我通常不会对学生的英语水平作一个整体的大概的评价，而是专注于通过明确反馈的方式纠正学生的错误。我认为，想说好英语最重要的就是了解单词的意思并明白如何使用它们。一个人不需要掌握巨大的词汇量或是完美的发音，学会如何使用日常生活中比较熟悉的词是最重要的。
举例而言，与一个学生进行一次五分钟的对话，并且在这一过程中无法找出学生任何的the, an ,a这一类冠词错误会令我印象深刻。
对于有机会与英语母语者进行交流的英语学习者，我的建议是尽可能地让母语者纠正你在语言表达上的错误，而不是仅仅从他们口中得到“你的英语很好”这类评价。只有这样，你的英语水平才会进步。
希望我的回答可以帮到您。
