The Cyrodiilic language as it appears in names has always been heavily Latin-influenced, with some English and somewhat-European words used freely. There is no official Cyrodiilic language, but we can assume from its history that it is a combination of Ayleid and Nordic, with some surviving influence of the speech of the early mannish and beastfolk tribes of Cyrodiil, and in Nibenay will have a splash of Akaviri influence from the Second Era.
The reason why Oblivion's Cyrodiilic names appear different is likely because, with the Imperials being at the fore of the game, a greater quantity and diversity of language is required, and so besides the Latin and Romance languages they take influence from there is an element of "generic fantasy" or "from scratch" naming, and some English names used directly or permuted.
It could also be a genuine change in the language and naming conventions of the province, at least in the gap between TES IV and V.
For coming up with in-universe names for the Cyrodiils, I would tend to stick with the faux-Latin of Morrowind, perhaps with Slavic or Germanic influence on Colovian (and some genuinely Nordic names) and a touch of south Asian influence in lower Nibenay.
As for a true reconstruction of the Cyrodiilic language, based on in-game examples and its history, http://www.imperial-library.info/content/hrafnirs-languages-nordic#Old%20Cyrodiilic may interest you, along with Hrafnir's other brilliant contributions in that thread.