Repair german language files; make "Select media" translatable

Wordpress on a LAMP installation seemingly ignores .mo files if they're not conforming to the standard "package-ab_CD.mo" format.

The original german translation files had the suffix "-DE_de.mo" instead of "-de_DE.mo", making the german translation unavailable. This change renames the .mo and .po file.

And because Christmas is a-knocking and I decided to help brush up the german translation (coming soon) I've found and i18n'd what I think was possibly the last hard coded string.