I've always viewed the Parliament and the Emperor as competing for power, in a way. Officially, the Parliament holds the power, but unofficially, there's a struggle within the Vasudan government over who really holds power. I can see multiple political parties, and at least one is a Royalist, which pursues restoring power to the Emperor, by legal and political means.
I think there is a general cult of the Emperor, but it's not very potent (widespread, yes, but not potent). This explains the language thing, if they didn't revere the Emperor at least a bit, then why bother with the language thing.
That said, the Imperium has been usurped, probably long ago, by the Parliament that held power until the Great War. In many ways, the Emperor still doesn't have power, but he does have influence, and that can mean a great deal. When the Shivans arrived, however, that influence increased to the point where the Emperor could actually dissolve the Parliament. With that, the cult of the Emperor returns to the forefront, and becomes much more prominent.