I don't know, I'd just put "APA citation style" into google and see which guide you find easiest to use/
What are they for?

It's a guide for correct writing, citing, referencing sources, footnotes and endnotes, that sort of a thing....
Actually, looking into a few books that were at a hands' reach. More often than not the titles are not even translated, just used in the original language. If you're using a translation of the book, go by the translated title (again, refer to the APA style for help on that), if you're working with the original, go with that. Just whatever is on the cover of the book. I only translate titles when I really need readers to know the translation of the book.
What is the article you're writing? Is it a college or high school paper? Or another purpose?