Because 7-bit ASCII didn't include accented characters used in many European langauges, there were national changes. The Finnish variant replaced {|}[\] with äöåÄÖÅ.
Which, btw, is why those symbols are acceptable as IRC nicknames (and why { is lowercase [, i.e., {some|one} and [some\one] are two equivalent nicknames). IRC was invented in Finland.
One might guess the people who decided on this replacement were not Unix programmers...
The lack of brackets, caret, tilde and other ASCII special characters on various localized keyboards was a real problem in the 1980s. The C language standard solved it by introducing trigraphs:
Of course you could still use {} etc, they just might show up as localized characters in your source code. There was no character set conversion involved at the source code level, your terminal font just might have had the glyph for ä in the place of {.
The people who designed the Finnish keyboard layout were definitely not programmers, though: https://kbdlayout.info/KBDFI/
Ditto with the Spanish (es) layout, they layout looks more apt for journalist and writters than programmers. I just switch to the us keymap with the compose key bound to right menu/right win key, so I can type áéíóú with compose key + ' + vowel (not pressed at the same time). Ñ is more cumbersome (compose key + ~ + n) but I can adapt XCompose under BSD/Linux for that.
