I'd say that it really depends on which foreign languages you want to learn about. I've never read the book mentioned by Ulrich, but my personal experience (as the DTP/prepress guy for a translation firm specializing in languages spoken by refugees) leads me to believe that the only way you'll learn about this stuff is by hacking through it yourself. I mean, Uniscribe is covered by the book, but because it's an MS product, it will talk about Uniscribe without mentioning the drawbacks. I don't imagine it'll say "Khmer script? HA! Forget about it!" However, that is the truth - MS products make computing or publishing in Cambodian very difficult. (weeeell, Cambodian is just a difficult script, so it's not ALL the fault of MS.)
Here's your rule of thumb, Klaus: If it's a language spoken by a people or culture that tends to 1) be affluent, and 2) speak English as well, you'll probably find it covered on the web, or in print. If it's not a language like this, then you'll literally have to go to primary sources - the professionals who do it.
For instance, if I have a tough Khmer/Cambodian question, I go to Sary (www.sary.ca), who is a Cambodian translator who made some fonts for Cambodian script. If I have a tough Lao question, I go to John Durdin (www.tavultesoft.com/lswin), who wrote LaoScript for Windows.
So, tell us what languages you want to know about, and I'll suggest some resources. In the interim, you may want to read the forums at www.proz.com, which is a kind of translation-industry gateway site. They might be able to answer your first question ("Which applications support which technologies"), but they'll certainly be able to answer your second ("how to get from one platform to the other without losing encodings, diacritics etc.").
Furthermore, you may want to fire a question at me, if the language you want to know about is spoken by a people who have been granted refugee status in the US. (RusSpaVieChiKorKhmLaoScrAraFasPusTirAmhSomRum and I'm sure I've forgotten to mention other languages that we handle on a regular basis, and others that don't have an ISO 639 code, like "Bosnian").
So, is your question about software development? Or implementation?
-j
ps If you know of resources, please post 'em!