Which keyboard are you using? It's impossible to accurately detect keyboard layout in javascript, but I do provide a option to select keyboards. Unfortunately, the only ones I've had time to implement so far are US QWERTY, UK Extended QWERTY, FR AZERTY, and DEU QWERTZ.
There is a small bug that I haven't fixed yet that requires you to look away from the editor to make the drop down lists on the instructions page work.
As for other languages, I have a tool at https://primroseeditor.com/keyboard_test.html that can put together the code pages that I use for this. It supports dead keys for typing umlauts, but it can be a little fiddly to use. I've been using the Windows on screen keyboard to make them, so I don't know how well it maps to reality.
Unless you mean using alt codes to your Unicode characters directly, no, don't have that feature yet. To the list!
