Which variety of English would be appropriate for writing a letter to the Minister of Education in which you raise your concerns about the quality...

In each English-speaking country, there are varieties of English used, mainly for spoken communication. To write a formal letter to the Minister of Education, you would want to use the Standard English, which refers to the written and spoken English used as the normal means of communication for business and educational purposes. In many parts of Great Britain, the Standard English is often referred to as the "Received Pronunciation" (or the Scottish Standard English in Scotland). In the United States, Canada, and other English-speaking countries, there is a Standard English used for news broadcasts, written media, and business communication. This type of communication does not use informal language or slang, and it requires proper punctuation and grammar.

The reason to use this form of English is that it is widely understood by people in different parts of the country (whether in Great Britain, Canada, the United States, or another English-speaking country). In addition, if you want the Minister of Education to understand your concerns and take them seriously enough to consider acting on them, you want to express yourself in the manner in which educated people write. You want to seem authoritative enough to have concerns the Minister of Education will consider valid.