Sometime around 1500 years ago the Anglo-Saxon dialect of Proto-Germanic underwent palatalization which, among other things, shifted /k/ → /g/ This can be seen very visibly in English between duplicated indigenous West Saxon words and Old Norse loanwords (which weren't palatalized) like "shirt" "skirt" and "ditch" "dyke" Because of this we can say, to a pretty good degree of certainty, that Æthelwulf of Wessex would've said "glug glug glug" and Alaric the Goth would've said "gluck gluck gluck"