Szenario:

Create a new page on the web, enter an umlaut in the page title, i. e. "schön".

The URL generated looks like this: "wiki?openform&page=sch%C3%B6n".

The title displays this "schon" (no dots on the o).

A computed text on the form with the formula @UrlQueryString("page") shows the correct text: "schön".

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Somehow the shared field Subject in "General wiki fields" can deal with international characters, although the formula is @UrlQueryString("page"), too.

-> Suggestion: Change "Web\Page header" to display a computed value @UrlQueryString("page") when document is new and edited instead of "Subject".