Is English the most illogical language?
No. There is no such thing as an illogical language. English does have a spelling system that seems at times illogical, but spelling and language are two entirely different things.
Why do you say that English language has an added advantage of becoming the world most dominant language?
Not really because there are countries that have their own languages. But because of global communication, the English language is becoming more relevant. The English language is the most common language in the world, as it is used in official business worldwide. We still have some other languages that are widely used (e.g. French, Arabic, etc.). Mandarin is the most spoken language by native speakers, but English is the most spoken language by total speakers.