I'm not the OP, I was just interested in how it would play out.
Well, the royal you.
How different would a Europe be in which Clovis successfully codified Germanic paganism?
Well, there'll be some good potential Plot to work with from all the many Germanic Heathens whom are
not under Clovis's control, and how
they feel about things. Some accepting the authority of Clovis's church structure, others ignoring the arrogance of the Franks, thinking they can know the truth of the Gods. And others still who take such offense to the specifics of Clovis's doctrine (or just hate Clovis) that they decide to have their
own reformation, and this time they'll do it
right. Saxony's a good pick for that one.
Arianism could well just
stay the dominant form of Christianity in Germania; with a big Heathen polity in France, the Nicaean church is going to have problems enforcing their canon on the heretics north of the Alps in general. How important the Arians are in Germania, that'll be up to the writer.
A Codified Germanic faith could well have a strong edge over Christians when it came to converting other pagans. You could, for example, see culturally Germanic and religiously Christian realms scattered around south-central Europe, but have huge swaths of the Slavic world worshiping the Germanic Gods in some form.
How many of his subjects were already Christian? Were Franks the majority of the population in the area they ruled?
I am not aware, tbh.
@Sachmis do you know?
The Franks were mostly germanic pagans, but that's just (roughly) modern Belgium. Clovis's Empire covered most of Gaul.
However, all is not lost for your dreams of Clovis codifying the religion of his forefathers! Christianity was far from a perfectly unified thing in those times either, with loads of groups out of communion with the Nicenes all over the place. Furthermore, the lands had only converted to Christianity in bulk at all
very recently. There would still have been pagans, crypto-pagans, and pseudo-pagans out the wazoo.
Depending on Clovis's talents (or the talents of people he delegates to), he could play his majority Christian subjects off each other by magnifying their differences, and unite his deeply divided minority pagan subjects behind himself(1) by magnifying their similarities. "Mars, Mithra, Tiwaz, these are all names for the same Great God of Victory!" You know, syncretism, except only one point of view is written down.
It would be a complete administrative nightmare, but not
necessarily undoable. Kublai Khan could have pulled something like this off, but I've got no idea if Clovis had the chops. Still, the
really important bit is getting the idea of Codification as a Necessity out there. If Clovis's attempt fails, but a powerful Saxon King pulls it off thirty years later inspired by Clovis's work, that's still a reformation.
Also, I don't know if this is economically plausible, but if Clovis conquered in the opposite direction and managed a similar breadth of conquests in Germanic Heathen lands as he managed in Christian lands, the administrative problems with the lead up to reformation I was just talking about go away. It would also allow for a
much more united church for the Germanics, although schism is inevitable regardless over the kind of area they were spread around at that point.
(1)Or more likely, whichever Goði he wants running his new church while he plays Good Cop with the Christians. "I'm holding the pagans back as best I can, but you've gotta give me something to work with!" etc.