I am not sure, if I understood all of the Google translation of your post...
And you are right, that eCart etc. should be simply translateable into different languages. I've made that suggestion to WA already in another post, recently. (showthread.php?t=26239)
UTF-8 definitely works. In German we have to deal with special characters, too (for example: "ä" ä "ß" ß ...).
I'm doing all my databases and websites using UTF-8 with no issues.
So maybe you need assistance here. I don't know if I could help you, but am sure somebody on this forum can.
As for the Dreamweaver startup error, that should be fixed quite soon. WA already announced the update.
I understand your problem with close deadlines of course.
What I did, just in case, I only installed the new extensions for DW CS5 and left the old ones for CS4. So I can switch between the different versions. Somebody (Ray or Jason) mentioned to just add another Windows user account to handle different settings. That's a good idea, too.
I hope you can finish your project in time and get over the trouble you got right now.
Greetings from Munich/Germany