`tr 'A-Z' 'a-z'` will only convert non-accented characters. Switching to
`[:upper:]` and `[:lower:]` adds support for accents.
See https://github.com/koalaman/shellcheck/wiki/SC2018
Additionally, printf's character splitting does not support accented
characters, so output isn't as expected. Using bash's variable expansion
syntax instead will correctly get the full accented character.
Noah Gorny
Nils Winkler
Zhao Li
Dan Wendorf