In Polish we have 9 such characters and most people use just so called "programmers keyboard layout" which uses left-alt + letter to do the accent.
E.g. alt + e = ę, alt + l = ł (with a one case where we have two different accents for a single letter: z, so we use alt+z = ż and alt+x = ź, the second letter is less commonly used then the first one)
20-30 years ago there were some strange keyboard layouts that didn't use alt, but hopefully they were forgotten.
on the right of the keyboard: ù
but that's enough to want accents and symbols on the number row by default (&é"'(-è_çà) and numbers when pressing shift.
I think that's the reason that bépo (a French variant of dvorak which allows easy access of both common accentuated keys and numbers) is more popular among French speakers than dvorak is for English speakers, proportionally.
I have never seen anyone use an Alt+number to get these, I personally default to EN layout and switch only when I write in local language.