回复：请问单身老猫， 立遗嘱的事情

Every state requires a person over 18 years old to make a valid will.
You will need an attorney to make a will. Formality is more important than content. If you want to save a few bucks, go to staples to buy a statutory will and follow the instructions therein.
A will is an ambulatory document and you can change it any time. This applies to joint will as well.

Whether and how a probate court will treat property in china depends on many things. Normally a valid will made in the US would also be valid in China. However, a US court may not have jurisdiction over the property in China. The court may not know the Chinese law, which governs real property there. Most importantly, there may be conflict between Chinese law and American law, in terms of how the property is willed, distributed, and how it is taxed. You have to consult an estate planning attorney to find out.