This is a completely new adventure with other languages.

Well, Vietnamese support is available in many fonts - no problem there, stuff that ships with the Creative Suite like Minion Pro and Myriad Pro will support Vietnamese. You also get some Chinese fonts (a limited selection), but frankly, it's hard to typeset Chinese. It's a culture with a tradition of literacy and calligraphy that is twice as old as Christianity. Its typographic rules are more complicated than ours; just as an example, they have more kinds of commas than does any Latin-script language. And if you set that type with an English-reading eye, you will make many mistakes. So, you stand a pretty good chance of embarassing yourself and alienating your readership if you dive in without doing some learning first; much of the Chinese-literate population is going to be more offended by poorly-set text than your average English-reading population. I spent years buying Chinese books and taking them to my translators, asking them "Hey, what the heck is this typographical convention?" in order to acquire the basics of how to format Chinese text correctly.

Cambodian, though... you are starting your adventure with one of the most complicated writing systems currently in use. It's so complicated that you can't even begin to typeset it in InDesign in contemporary fonts without using the World-Ready Composer. And there aren't spaces between the words, and no hyphenation is possible or permissibile, so you need either to be able to read the language in order to break the lines correctly, or to be able to prepare files for assignment in such a way as to be absolutely certain that the margin width used by your translator is exactly the same as the margin width in your target document. And your translator needs to know enough to use manual line breaks at the end of each line, or some convention that allows you to wrap the lines yourself without inducing errors.

This working method doesn't even account for text expansion. The total character count for the Cambodian translation will likely be 120% of that of the English, so one way to handle it would be to make Word files with the size of your text areas, tell your translator "Your translation must fit in this space, and we will take delivery in PDF only." Then you could color-correct the PDF in Acrobat (because it'll come out of Word as rich black, of course) and place that in your InDesign file. This is probably the only way to get it to render correctly.

Basically, unless you're willing to work with placed PDF files that you can't edit, it's over your head. Job it out. The Cambodian portion of your project, I mean. You can learn a hell of a lot about typesetting Chinese by posting lots of questions in forums and counting on helpful bilingual type-savvy people to teach you stuff for free. So you can almost certainly handle that without inducing significant errors that will prevent comprehension.  And it's remotely possible that you can build a workflow that will get you two-column Cambodian text that is not studded with errors, but at this stage I sadly would have to bet against.

Sorry, don't mean to be offensive or to demean your abilities. But this is what I do every day - I do complex-script DTP for a nonprofit translation firm, I specialize in the hard stuff like minority Central Asian languages and SE Asian languages - and I would advise against tackling Cambodian in your first multilingual design project.