Is this correct in English? Check grammar, please

No, it's rather poor English . . . let's see if we can fix it up.

I began to study a foreign language in the fifth grade. It was the English language. I had three hours of foreign language instruction each week in my curriculum. Many pupils study carelessly, as a result of which we did not keep to the lesson plan and I missed a lot. (I couldn't really make out what you wanted to say in the previous sentence, so i hope this is what you had in mind.) In my country foreign language instruction is not considered very important. (Once again, i'm not sure what you were trying to say, so i made my best guess.) Many native speakers of a language do not know much. (That's an awkward sentence even after attempting to fix it--once again, i'm not entirely certain what you are trying to say.) Learning takes time, which can better be spent on learning profile subjects. But it doesn't mean that foreign language learning is not worthwhile. Learning a foreign language has many positive aspects. One primary aspect is broadening your mind. (I deleted the entire succeeding sentence as it is nonsensical and rather embarrassingly obvious--of course you can't understand books, song lyrics and films in a foreign language unless you understand the language.) Communicating with foreigners can be enjoyable. Learning foreign culture has expanded my knowledge. Foreign language learning can make travel, getting jobs and learning abroad possible. (That is also a rather nonsensical sentence, in that you are unlikely to benefit from travel, a job search and educational opportunities if you don't spake the language of the country to which you travel.) I think that learning a foreign language should start in the first grade of primary school. At that age it is easier to assimilate language instruction.. Students need to communicate more with speakers of the foreign language, invite foreigners to go out or to come to their homes, and just listen. Beginning in high school, students can benefit from travel abroad to practice the language. (I removed the word voluntary because i doubt if anyone is going to kidnap you in order to force you to study abroad.) I think many parents would agree to pay for the trip. To sum up, in the modern world, learning foreign languages plays a very important role, and requires spending a lot of time on it in school. I am very sorry that he paid little attention to it. (What? He who? If you are referring to yourself, you would write: "I'm very sorry that i paid little attention to it.")

Americans, at least, rarely use the word pupil, they are far more likely to use the word student. I can't speak for other non-American native speakers of English.