To add characters to your keyboard without changing its layout you can use Microsoft Keyboard Layout Creator.
I built a very simple one. Using the portuguese keyboard layout i added the following german characters:
- ä = ALT GR + A
- ü = ALT GR + U
- ß = ALT GR + S
pt-de2.klc – My source file. To use it, in the program click file – open source file – choose mine – you can make the changes you want or keep it the way it is – then click in project – test – test your carachters – click again in project – validate – check the log for errors – click in project – Build DLL and setup package – it will create a setup file for you to install – after instalation go to your regional computer preferences – change the keyboard to the new one.
You can also open an existing keyboard layout instead of mine, change it and save it with another name.
Although not very user friendly, you can check some character codes on this page, the site lets you choose by country characters and you just have to check the code for the key where that character is in that country's keyboard. Some characters codes are also in the program's help files.