Doesn’t seem to be so bad. All official plugins (except for one or two new ones) have been translated by a translation agency quite recently.
“Customize Text” isn’t really made for translating Discourse. It’s – as the name implies – made for customizing text.
You could help translating at translate.discourse.org. It has all the filters you need and please add a comment to a string if you aren’t happy with a translation that has already been reviewed.