ice-9 i18n string-locale-upcase

[Simon Albrecht]

Hi everyone,

I wanted to set up some customisable headings using #(string-upcase 
"string"), but it doesn’t work on German umlauts, so I came upon 
string-locale-upcase on this page:

https://www.gnu.org/software/guile/docs/docs-2.2/guile-ref/Character-Case-Mapping.html#Character-Case-Mapping

However, I can’t get it to work. To this example file:

%%%%%%%%%%%%%%%%%%%%%%%%
\version "2.23.5"
#(use-modules (ice-9 i18n))
\markup \column {
  #(string-upcase "üß")
  #(string-locale-upcase "üß" "de_DE")
}
%%%%%%%%%%%%%%%%%%%%%%%%

Guile says: “no code for module (ice-9 i18n)”.

Why? Can I load the module another way? Will it do what I want? Should I 
use another tool? ;-)

Thanks in advance,
Simon