I have a friend who is from France. My friend, like most people from non-native English speaking countries, learned English at school and has had to use English both in his work and when he travels. However, unlike my Korean friends, my French friend has never attended a language institute to learn English, all the English he knows was either learnt at school or has been picked up as he has used English in his everyday life.

My friend has excellent English. Yes, he makes a few grammatical errors, and yes, sometimes the word he wants to use he has difficulty finding. But he never thinks “I can’t speak English” English to him is a part of life and something that he has to use from time to time. It is a little like driving a car. He can do it when he needs to, but it is not his whole life.
Unfortunately, I find in Korea that people are striving for something called “perfect English”. Perfect English does not exist. English, by its very nature is continuously changing and because it is spoken by far more non-native speakers than native speakers has so many variations it really is impossible to figure out what “perfect English” is.
However, what I have noticed is that the really good English speakers do not care about perfect English. They use English to communicate and that is it. To the really good English speakers English is a tool to communicate with their foreign friends and business partners. They don’t care about occasionally not knowing a word or how to express themselves – they know they can describe the feeling or word to their partners and they will eventually understand. They do not care about making a few grammatical errors because they know their partners will not notice the occasional mistake.
This has made me realize that the difference between good speakers of English and the not so good speakers of English is “attitude” Those people who have the “I only want to communicate in English” attitude are the ones who speak good English and the ones who worry about making a mistake or are trying to speak perfectly are the people who struggle with English.
When it comes to speaking in English you need the attitude of “I can do it” rather than “I cannot do it perfectly” Perfect English does not really exist, and by the time you have found something close to near perfect English it will have changed anyway.
So, stop worrying about making mistakes – mistakes are natural anyway. Start communicating and enjoying English. That attitude will serve you much better and will enable you to achieve greater communication success than worrying about whether you have used the correct preposition or article.