An Etymological Dictionary of the German Language/Flagge
Flagge, f., ‘flag, ensign, standard,’ borrowed, like most words with gg (see Dogge, Bagger), from LG. and Du. in the ModHG. period; comp. Du. vlag, E. flag, Dan. flag, Swed. flagg. A modern Teut. word not recorded in the earlier periods. In which of the Teut. maritime tribes this and other nautical terms were first used we know not, for the earlier history eludes us. Since, however, AS. preserves the earliest forms of a number of nautical terms which are afterwards found in all the cognate languages (see Bord, Boot, Helm (2), Spriet, &c.), the silence of the AS. records — no term *flacge is found — may be accepted as a proof that Flagge is not native to England.