I need to design two WordPress websites, both with contents in three different languages. One of the clients wants to write the contents himself (in different languages), but the other simply wants to write in his native language and have Google Translate generate the translations. I want no widgets nor obtrusive UIs: just a few hyperlinks to change languages. A bookmarkable URL is also necessary, to force the proper language to be loaded on page load.
What are the best practices for multi-language contents in WordPress websites I should follow in these situations? How should I develop these two different multi-language setups?