English is widely spoken and widely used in all the countries, especially in the business communities.  Even though you will be able to conduct most of your business in English, it will always be a plus for you to be able to speak at least a little of the local language

Time and money is important in developing and establishing your business in East Asia. Both required in developing your local business support services, arrange for and receive necessary local government permits, promote your products, and meet your local business contacts and prospective clients. 

Having a local associate, agent or employee will provide you assistance to you as you work your way through the local business, political, legal and cultural system. Local associates who speak the language can help get you from point A to point B.

East Asia countries have many cultures, customs and religious practices to be aware of. There are many similarities in working with the people and respecting the cultures in each of the countries. There are also many differences. Knowing and applying these social and religious customs and practices will certainly help you be successful in your business activities