It's definitely not a perfect solution, but it has worked well for me so far.
This is a horrendous layout. Bonus points for it being slightly different on Mac and PC.
I have absolutely no idea how people can use this layout for programming without going crazy. I don't program full time, I mostly do sysadmin work, and even if I don't think that typing speed is a limiting factor for how much code I can write, I do find it extremely annoying to type certain characters which are used quite often.
Regarding language I type equally English and French so I absolutely love the Mac OS international layout: QWERTY so everything is where you expect it but with ALT I can get pretty much every French character I want, easily. This could probably work for German, too: ALT U + U = Ü. ALT + S = ß. I'm not sure about other nordic languages, though.
I love this so much that I configured my linux and windows pcs to use the same layout. Some characters take somewhat longer to type (three different key strokes for ù instead of one) but I guess that for someone not writing exclusively french prose the tradeoff is completely worth it.
If you're typing numbers frequently and don't have a numpad, then it seems like that would be a worth while investment.
I find the physical shape of the keyboard to be a much more important factor than the layout. Tilted splits are where it's at for me.
US International keyboard layout does this to in Windows. It seems the only type of keyboard that doesn't do it is the standard US keyboard, but that one doesn't have a Euro sign. I'd like to have a board with a Euro sign, but without messing up my quotes.
What would be ideal for me is if I could type alt+quote to make it an accent over the next letter. Or even better, the latex way: \'e.
I would love to know how to customise this in various OSs. I suppose it should be possible.
As a bonus, you can actually configure your own sequences for letters that you need often. For example, I have Compose ,s,h bound to ¯\\_(ツ)_/¯, Compose,g,<any letter> bound to produce Greek characters, and Compose,t,q bound to my username.
XCompose is available on Linux using `setxkbmap -option compose:ralt`, on Windows using WinCompose, and there's probably a way to do it on OSX but I refuse to support that particular company on moral grounds so you're on your own.