Traditional Japanese manga reads from right to left (the reverse of English which reads left to right). In original manga-style books, the action, speech bubbles, and sound effects are all written in this direction. When you open the book, you start at the back of the book.
Manga that has been translated into the English language, will state on the back cover :100% Authentic Manga. This shows that the book has not been altered from it's original Japanese publication to it's North American release.
Some manga that are released in North America have the format changed so that English readers can easily pick up a book and read left to right.
Here is an example of traditional Japanese manga
(the panels are numbered in boxes and the speech balloons are numbered in circles)