I've added a few more things to a sentence. I'd like you to check it.

I included another doubt.

1) In particular, we may be interested in two different types of two-week courses: one for students, whose level usually ranges from low intermediate to upper intermediate; and one for those Italian teachers (especially science, history, and arts teachers) who will have to teach their subject in English in two years' time and usually have a low intermediate knowledge of the language.
2) Why is the sentence "Write to me soon" possible whereas "As I wrote to you" is a mistake?

Sure, I can check the sentence for you. Here is the revised version of your sentence:

"In particular, we may be interested in two different types of two-week courses: one for students, whose level usually ranges from low intermediate to upper intermediate; and one for Italian teachers, especially science, history, and arts teachers, who will have to teach their subjects in English in two years' time and usually have a low intermediate knowledge of the language."

Regarding your second question, let me explain why the sentence "Write to me soon" is possible, while "As I wrote to you" is considered a mistake.

The difference lies in the verb tense used in the two sentences. "Write to me soon" is a simple present tense sentence, expressing a general request or invitation. The present tense is commonly used for general statements or actions that occur frequently.

On the other hand, "As I wrote to you" is written in the past tense. However, there is a mismatch in tense between "as" (which suggests a specific past event) and "wrote" (simple past tense). To maintain consistency, either "As I write to you" (present tense) or "As I wrote to you" (past tense) should be used.

In summary, it's important to ensure that verb tenses are used appropriately to convey the intended meaning and maintain consistency within a sentence.