Miland:

tiberius:I also wonder if Θεοτόκος can be easily rendered in Esperanto...

The Catholic equivalent 'Mother of God' can be rendered Dipatrino. It is used thus in the Saluton Maria, the Esperanto version of the Ave Maria.

Orthodox Esperantists, however might prefer Dinaskinto.

In byzantine liturgies which I have attended Theotokos is left untranslated, and I always assumed that was because "mother of God" has a slightly broader meaning. While Latin liturgies tend to use "mother of God", I usually hear "Theotokos" being used in slightly different contexts ouside of Mass by people familiar with the subtle distinction.

The wikipedia article on Theotokos has a good explination as well.