Yeah they could have just had a few actors doing different accents, actors do it all the time, ie: theres heaps of british actors doing american accents on american tv.
They could have just done maybe 5 sets of accents, American (Midwest or something with a hint of cowboy feel but not overkill), english, some kind of terrible european accent that'll serve for every damn EU country, Morgan freeman, and chuck norris Bruce lee for all of asia.
That should be sufficient to create some kind of illusion that theres people from different countries, while also pissing 90% of the players for having unrealistic interpretation of their accent.
They've sort of already put that in, except not for the soldiers. The researcher woman in the briefing has a thick French-like/European accent.
Also, having played some of the demo, I now realize why they stuck with such a limited number of voices. It's cause the soldiers talk in length during the god awful cutscenes, and there's probably a lot of them.
Some other things from the demo:
-Aliens initially drop some things that turn people into green stuff or something? Is that supposed to be like a Troll 2 thing where they change people into this stuff and eat it? Or is it supposed to be like the most inept bioweapon ever? If this was ever explained, then I must've skipped it.
-The briefing guy is a moron who cannot understand "hilfe" and needs dr. Frenchie to translate for his stupid ass. I do not want either of these idiots to say anything, really. The whole concept of adding a narration this explicit is completely misguided and cheapens everything.
-The speeches are horribly cliche and constantly insult the player's intelligence.
-The gameplay isn't bad at all (when looking at it as a separate tactical turn-based game), except it's hindered by horrendous cutscenes and "story" levels.
-Both levels presented are cutscene shooter design. The first is an over-narrated tutorial where you know what's gonna happen before it does and would totally avoid these things using common sense if the game didn't order you to do them. The second is a corridor. It's got like 1:4 ratio dimensions, and cover everywhere along the way. It's just there to present the three basic alien types and give each a short cutscene where they do something and the briefing idiots start blabbering something about them before you shoot them.
-Having to choose between two locations to go to is nonsensical. In the post-demo cutscene, they even refer to an XCOM team as "Alpha team", implying there's more than one team. So why do they send out only one team at a time?
On a few of your points:
1) The green stuff, I don't think they've explained it yet. It seems to me like it's designed to incapacitate large groups of humans, as they seem to appear on all the "abduction" missions, I'd imagine it's to make for easier transport. I'm sure more will be reveal in game.
2)I also don't understand hilife (german for help? If I remeber the demo correctly), also, I found the narration enjoyable, and gave a bit more life to the world. Also, not sure her accent is french, I thought it sounded more germanish, but I'm hardly an expert
3) Didn't feel insulted personally, not sure how you found them stupid?
4) Didn't find the cutscenes hindering personally, and since it was just the first two tutorial missions, I'd expect them to be more story heavy. i'm not quite convinced that complete freeform, no story is always the best way to go. It works sometimes, but sometimes I like a good story element.
5)Again, first two tutorials, of course it's over narrated, it's both the tutorial AND setting the scene and mood for the game. It's first contact! And the second is to ease you into the game. From the gameplay we've seen elswhere, the levels will open up, don't worry.
6) I like the concept of an impactful decission, while I hope they have some sort of explanation for it, I feel it works. Again, just my opinion.