Issue with Slovene unicode characters in search url

I think I reported that way back. It still doesn't work. It's best described with an example:

This url works fine:

accord://search/SSP°;Words?aba

This does not:

accord://search/SSP°;Words?oče

Even the URI-encoded form doesn't:

accord://search/SSP°;Words?o%C4%8De

This is how it looks in Accordance:

German umlauts work surprisingly well. But the following Slovene characters do not: č, š, ž.

BTW: I can type and search “oče” just fine in Accordance, so it’s a problem with the URL scheme.