I created a new StarDict dictionary from the BGL file with the official StarDict Editor and it appears to be working fine with the latest stable KOReader Kindle version.
If it doesn't work with your Kobo, you might have to install the latest stable Kobo version or if you've installed the nightly build you might have to downgrade it to the stable version.
Either way, if it doesn't work, you may want to report this issue in the KOReader forum.
As of June 2015, KOReader doesn't support inflections.