English has a wholly pagan week, but the middle day in German has become a neutral descriptor. And in Portuguese, neutral or Christian terms have driven all of the gods out of the week altogether. It is posited that we could take two cognate languages and tell how long ago they diverged by counting the percentage of basic words still cognate. Still, though language is evolutionary and biological, the presence of truly cultural elements means that glottochronology is a terribly inexact science. Yet of course, Portuguese and Spanish have diverged relatively recently.
Cultural forces act more quickly and unpredictably than any biological force.