In German (de) Firefox CE 58.0.2, the info texts from Mozilla explaining the new tab page or trackingprotection are displayed in English language. I assume that %LOCALE% variable is not set to de-de for German? Other things are localized.
With FMFirefoxCE-58.0.2-de.msi I see in about:config that general.useragent.locale is "en-US", in the previous versions (latest we currently use is FMFirefoxCE-54.0-de.msi), this is "de". But even if I change this manually, the texts remain untranslated in English. So, something is wrong with the current German version.
I just downloaded FMFirefox 57.0.4-de for testing, the general-useragent.locale is "de", but the info texts are also not translated.