“Every coin has two sides”
Actually, every coin has three sides; however, a coin always lands on only one side (unless there is deep grass etc.). There are various essay types that require the writer to take a side. In such papers, the writer needs to use the overall essay structure as well as language to assert the side being taken. The marker of the essay assesses based on how clear the writer’s side is and how well it is supported. Any philosophical disagreements between the writer and the marker over opinions are irrelevant in the context of English courses and assessment. Nevertheless, if a side is not well supported, it is likely to be assessed lower.
“I don’t have enough vocabularies”
Back when I lived in Japan, there was a humorous cartoon in a magazine for expats, which contained the caption: “This is Taro Suzuki and he has memorised the Oxford English Dictionary five times over, yet he is unable to speak or understand a single English sentence”. The point here is that words are wonderful things, but in order to meaningfully communicate, they are placed together in certain ways i.e. phrases and sentences. Further still, the intended message of phrases and sentences can be affected by how it is delivered (intonation, stress etc) and also context.
This is a controversial issue, so hedging is likely to follow… Translation is not an exact science as language encompasses elements of society, history and culture in addition to context in the expression of language. An example of this is the Chinese word 关系, often translated as “relationship” in English, although this does not fully illustrate the complexity of the concept. At this point, Chinese writers would ask a question like “So how to overcome this?” In order to better express ideas in all languages, it is necessary to have enough wider knowledge of the wider context in which the language is used. Thinking in the language you are trying to use rather than your first or most comfortable one is the best approach to take. Yes, it takes time and patience, but it creates the opportunity to achieve in and with English.