How can one ascertain whether chocolate imported from abroad, such as "Twix" and "Kit Kat," is halal or haram, especially since the ingredients are not clearly listed?

The basic principle concerning all foods and drinks is permissibility, unless there is evidence to prove their prohibition, based on the Almighty’s saying: (He is the One Who created for you all of that which is on earth), and the Prophet's (peace be upon him) saying: "What He remained silent about is pardoned." So, if its prohibition is not established by a text, a general religious principle, or a sound analogy, then it is permissible.