As previously discussed in #19469

The lowercase, uppercase, and the not yet merged titlecase function do not handle the special casing conventions outlined in UTR#21 correctly.

Examples

julia> lowercase("OΔΥΣΣΕΥΣ")
"oδυσσευσ" # wrong, uses the non-final sigma
"oδυσσευς" # would be correct, uses the final sigma

EDIT (2021/03/19): This example has become obsolete due to a 2017 change in German orthography.

julia> uppercase("Spaß")
"SPAß" # wrong
"SPASS" # would have been correct until 2017