Why is it trivial?

The ä and a sounds in Swedish and Finnish are swapped; and they're direct neighbours (with compulsory education for Swedish in Finland, no less).

But within each language it is well defined.

Between languages, even the letters have different uses. Diacritics can be used to signal a different sound or the tonicity of the word (at least in the languages I know those are the two uses).

I don't understand what this thread is all about. English doesn't need accents because there's no universal meaning attached to each one? That doesn't make sense.

Do you have any examples? As a Finnish speaker the Swedish "a" sounds the same. "Pappa", "framtiden" etc.

It's "ä" and "e" which have swapped uses, but it's not exactly consistent (e.g. "Järnvägstorget" where first ä is close to the Finnish ä, second ä is closer to e but so is the e at the end)

Ä in Swedish is an æ sound.

Ä in Finnish is a pitched A sound, like the A in “cat”.

The pitched “a” in Swedish is the default one.

Wikipedia lists both "cat" and the Finnish "mäki" under æ: https://en.m.wikipedia.org/wiki/Near-open_front_unrounded_vo...

Do you have some example words that would show the difference?

Well, mostly hearing people say the words will be telling.

Gävle in Sweden: https://forvo.com/word/g%C3%A4vle/

Linnanmäki in Finland: https://forvo.com/word/linnanm%C3%A4ki/

In the Finnish example you can hear both the soft “en” (linnan) and the higher pitched “” (maki) which is triggered with umlauts;

Where the Swedish A is softened by umlauts in the Gävle example.

That's an american cat then, because that sounds crazy to my ears

(how did I get downvoted for this when I literally lived in both countries)

not just neighbors by country. a not insignificant proportion of finns speak swedish natively