Translations to some languages not working properly

I tried to implement more languages to the translations example (https://doc.qt.io/qtinstallerframework/qt-installer-framework-translations-example.html). 

I tried a few translations and ended up with two results:

• Works 100% - German (de), Polish (pl) - implemented in the example
• The only working translations are the manually created translations (page.ui + installscript.qs) and translations from xml file (xml:lang="") - Czech (cs), Japanese (jp)