Frankenstein and
zeitgeist, among other exceptions to the rule (notably
proper names, including
Fahrenheit), are of German origin - and 'i before e' is NOT a rule of the
German language. German 'ei' is pronounced as the long 'i', while 'ie' is pronounced as the long 'e'. Hence,
"
Stein" (
shtine, stone),
"
weil" (
vile, while), and
"
Wein" (
vine, wine)
vs.
"
Wien" (
veen, Vienna),
"
vier" (
feer, four), and
"
Bier" (
beer, beer).