With just two or three Western European languages to write in, you can easily have grave, acute and circumflex accents, umlauts, tildes, plus a couple one-off letters (like ß for German, ç for French, or å/æ for Scandinavian languages). Combining those with every vowel they can apply to grows too much for the poor Alt key.
The US-International layout runs into this problem. Since Alt + A = Á, if you want to type Ä or Å or Æ in a single keypress you have to use Alt + Q, W, or Z respectively, which is hardly intuitive. And if you want À or Ã, you're SOL.
Dead keys (also in the US-International layout) solve this problem. I know which keys make the tilde, umlaut, both types of accents, and circumflex. If I want the bare symbol (or a quote in the case of umlaut) I press spacebar after the symbol key, otherwise I press any applicable letter to output the modified version. For example, I'm pretty sure there's a key combination for ç, but I don't remember what it is (Alt + C is ©); however I did remember that I could type it as ' + c.
The other main solution is to have a hotkey for switching language layouts - typing in each language will be slightly faster, but when I tried it I frequently forgot which layout I was on and had to stop, delete my mangled output, switch language, and type again. I find dead keys much more friendly to muscle-memory.
'àquele' is the preposition 'a' + 'aquele'. Grave accents are only used to mark contractions such as this, and the circumflex and acute accents - which denote differences in vowel quality and stress - are much more common, which is why it makes perfect sense to prioritise ease of typing for those two over the grave accent.
That's fine for ò I guess, but then how do you type ô, ö and ó?
But as has been said elsewhere, this thread is confusing dead keys, which have nothing to do with fonts: typing the ^ key followed by the o key enters a single character ô, with combining characters where the character ̂ followed by the character o is rendered as ̂o (which should look the same as ô) (edit looks like this works fine on my fixed-width font when editing, but not so fine on the regular proportional font when displaying the comment, it's sadly quite usual for fonts to mishandle combining characters).
Here, the issue is that the standalone non-combining ` (as well as ´, ¨ and ¸) is handled by this font as if they were combining, thus doubly confusing users with dead-key keyboards.
I'm quite glad of that, actually, it would be really annoying if we had to keep using modifiers every two words. I know french people who use English keyboards, they just usually forget about accents totally instead of using dedicated modifiers.
It is probably easier for language that doesn't have multiple diacritics for the same letter.
In Poland we have only one such letter: z. The problem is solved by using 'x' for the other (less frequently used) diacritic type:
alt+z = ż
alt+x = ź
Which language, for example?
I'm french, we have characters with grave accent ('à', 'è' and 'ù'), and we do not expect the "` + a = à" behavior, as for one language.
EDIT: we do expect that "^ + a = â", though, but that's an other thing, and we have actually two ^ keys, one for our behavior and one for the usual behavior.