If you really understand the English passage 100%, there is practically no chance that you cannot render the equivalent meaning in Thai.
It is the degree of your language competency in both languages. This is simple. If you ever take a standardized tests such as Toefl, CU-TEP, TU-GET and you can earn the score at the range of 95-100%, I am sure that you will never have the problem of translating in Thai equivalent.