You touch a whole bunch of broad topics. You must be realistic, that a casual forum discussion won't answer them to any depth.
> I am setting up a pilot-project to provide online courses to Burmese students living in Thailand .
That is good news. I follow the development of Burma and Tibet for decades, the two most repressive regimes in Asia and the lives of two Saints of the caliber of Gandhi or Mandela. If the web can influence the outcome of this struggle that would be fantastic!
> The courses will be in english and I want to use Forums, Chat, emails so that learners communicate each other and with the trainer.
Moodle offers much more: Check "Using Moodle"
blocks 2 and 3 ("Moodle core code" and "Moodle contributed code").
According to http://moodle.org/mod/resource/view.php?id=948
Burmese is not yet supported, may be you'll find the ressources one day.
> On Moodle.org many technical problems are reported, and even when Moodle is hosted by a company.
What do you expect? Moodle is an advanced tool, show me a tool with no reported problems.
> So I wonder if I really need to use a CMS (Course Management System) like Moodle (or other) ?
Only you can answer that. This is not the commercial world where you'll hear "We know what you need, our product of course!".
> If my students have already the content on their computer, they will use Internet to get other resources,
Good to know that the exile Burmese have Internet access in Thailand. The reports coming out of Burma are horrible.
> they will be able to Chat through Yahoo Messenger (or other), and I found a partner that can use his Website Forum place for forums…
Yes, if your "customers" are at ease in the net, they'll find those and many other services for free or almost free.
> So, Why do you think I need a formal CMS ? maybe If I want to use other CMS options (test, quizz…), If I have more students ?
Again, you should answer that question yourself. As I see it, you want to reach a community. If each go to a different chat for forum, where is the community? Or, as Séverin has pointed out, if they login to different places for different services, will they be happy?
> I just want to focus about pedagogy and communication…
The best thing then is to do a test run on Moodle!