Can you tell me if rooibos tea contains l-theanine?

No, it doesn't: Rooibos tea is made from a different plant (aspalathus linearis -- a broom like member of the legume family) than regular tea (camellia sinensis). Theanine, is found in camellia sinensis -- from which green tea and others are made -- and certain mushrooms. Though it doesn't contain l-theanine, rooibos does contain other healthy polyphenols, flavonols, and antioxidants. And it tastes good too.