To insert some characters like ñ, I press and hold the “n” key to get a popup, and then I hit the 1 key to get an ñ. This works in my main Scrivener windows and in other Mac programs, but doesn’t work in Scratchpad for n/ñ or any other letter.
I can insert characters with the character viewer (ctrl + cmd + spacebar, find character, click it), so Scratchpad can accept and display special characters correctly. It seems like it’s not registering or responding to the long-press, though. It displays the regular “n” (or whatever character) like normal when I first hit the key, but never shows the pop-up.
I can’t give you any answer about why the long-press system isn’t working on the scratchpad, but did you know Opt-n followed immediately by n gives you ñ. Opt-n is the “dead-key”—I think that’s what it’s called!—for the ‘tilde’, so ã, õ etc. are easily accessible that way. Other accents are also available: Opt-e for acute; Opt-` for grave; Opt-i for circumflex; Opt-u for umlaut/diaresis; Opt-ç gives you ç; and many more.
The Opt-technique is part of the system. If you set your system preferences to show the keyboard selector in the menu bar—I’m not at my Mac at the moment, so I can’t remember the exact steps … it’s the first thing I do with a new machine—that gives you access to “Keyboard Viewer”, which shows all of the dead-keys and extra glyphs if you hold down Opt and Shift-Opt.
