Regarding the original issue: I will try to create a new build soon of current master natively compiled on Windows. It would be great if you could test it then.
Will test when I see a new nightly.
a) this is expected as the translation files are not included in the nightly build ZIP archive
Good to know. Next time I will check Github master before reporting an i18n issue.
b) I don't understand yet why there are issues with the icons ...
Normally the Nightlies work pretty well for me under windows. Sometimes when the new Nightly needs a newer version of GTK than the version of GTK that came with the previous Geany release then there are problems with parts of the GUI.