plainness

English Notes: 

Goblet: 17:19 And you shall not equate moderation (modesty) with submissiveness, because moderation (modesty) is based in undemandingness, restraint, well-educatedness and in plainness, in lenience, deference (honourableness) and patience; ...

English Description: 

online etymology: c.1300, "flatness," from plain (adj.) + -ness. Meaning "clarity" is mid-15c.; that of "open conduct" is from 1540s; that of "absence of ornament" is from 1580s.

simpleness or simplicity would perhaps be better

German Translation: