I'd like to buy some movie DVDs in Hong Kong, Taiwan and Japan. People here in the US are telling me to be careful because DVDs bought in those countries might not be formatted correctly for DVDs players in the USA making it impossible to view them in the US, Is this true?

I have also been told by some people that I can buy DVDs that are formatted to play in Cantonese, Mandarin with or without English subtitles? Is this true or is it only special DVDs that can somehow "switch languages"?

DVDs can (most are) marked with a "Region Code". All (minus an _extremely small_ subset) players have programming that allows them to play only DVDs that match the player's region code. This allows the producing entity (studio) to restrict what countries (theoretically) can play the DVD.

A better explanation of this can be found in the rec.video.dvd FAQ, at http://www.dvddemystified.com/dvdfaq.html#1.10

DVDs inherently have the ability to store up to 8 audio tracks, and up to 32 subtitle tracks. All players (as far as I know) have the ability to select which audio track, and which subtitle track, is played/shown. I.e., it's up to the studio what they put on. I've seen DVDs with as many as 5 different audio tracks, and more than a dozen subtitle tracks.

So, the short answer is there there's no short answer -- one DVD may have only english 2-channel audio and no subtitles at all, and the next may have English 2-channel, English 5.1-channel, Spanish, French, Italian, Cantonese, and Manadarin, and subtitles for all those as well as Arabic, Tagalog, and Korean.

Well, there are multi format (NTSC & PAL) and multi region DVD players out there you can buy. I have a Samsung DVK3211K which is one.

Otherwise, yes look out for Region compatibility.

Depending on where in Thailand and Hong Kong you buy the DVDs, they might not have a region code on them.

...and they may have a permanent Mandarin/Canton/other subtitle track displaying and/or the silhouette of a person walking out of the theater to get some popcorn....

It's not so bad these days - more likely a copy of a preview DVD sent to the press (or one of the people who helps decide who gets Oscars) that made it out to Taiwan, got copied and augmented with Mandarin/Cantonese/Arabic subtitles (sometimes all three at the same time).

I got a copy of The Two Towers from an outlet in Nairobi a few months before it came out officially (I couldn't wait) and it was perfect. Of course, I bought the original when it came out and then bought it again when the extended edition came out.