Negative questions are often impossible to translate, and are notoriously difficult for international readers. In many languages, people answer 'yes' where the appropriate English answer would be 'no'. Even one negative word in a question can destroy communication. When you ask a question, keep it very simple. Make sure you ask only one question at a time.
Double negatives are doubly difficult for international readers.
In English, two negatives make a positive. In some other languages, two negatives emphasise the negative. Thus an international reader may assume that 'not unusual' means 'very unusual'. Negative language is hard to translate and often causes grammatical errors. Negative language is confusing, because it is hard to think about non-existent things.