Using demo-project :
1) Switch to German locale
2) Change navigation title of any page
3) Go to site map and edit site map paragraph:

• used title: navigation title
• choose root page: /demo-project (or any other, but do not leave empty)

==> Site map does not display German navigation title for updated page(s)

This issue can be easily solved using I18nContentWrapper in SiteMapParagraphModel:
83: return new I18nContentWrapper(manualChosenRoot);

Maybe there is a better solution with STKUtil.getReferencedContent which may return i18n content when argument is also i18n content