In this case you the words are interchangeable. However, there are certain situations which are not true. "The ballon has expanded" -- correct. Incorrect if you substitute it for "increased". The number of ballons in the package has increased -- correct. "The economy has expanded" -- correct, incorrect if "increased" is used. I can expand my business. (offer more products to sell) I can increase my business. (make more sales) The best is to remember = "expand" = "enlarge". "increase" = "make more" The number of new languages is expanding! -- new languages have been discovered (perhaps in some remote areas of the world) The number of new languages is increasing! -- creation of artificial languages.

Expand: become or make larger or more extensive. Increase: become or make greater in number, amount, or degree. In fact 'expand' means 'increase' in size

After the big bang, the universe expanded. The size of the universe increased. If you inflate a balloon, it expands. The volume of air inside it increases, as does it's size. The number of languages in the world is increasing. Expand is more when a thing becomes larger, or more vast. Increase is when the number or things or the quantity becomes larger. As houses get bigger, their cost increases. As you become smarter, your knowledge base expands. Maybe somebody else can add to this?