That's because I hate writing two strings, one for the CLI and one for the GUI, so I just recycle the CLI strings in the GUI. It's sub-optimal, but since calibre already has over a 1300 strings, I think it's worth the tradeoff.
Unfortunately, "Metadata reader" is the string describing plugin type and the GUI just adds plugin to it when creationg the list. I'm not sure how that can be handled multilingually.
I'll fix the HTML fragments in the next release.