Month names collection / metastudy

[ReneZ]

While looking into this, I came across Français et dialectes chez les auteurs belges du moyen age by JULES FELLER.
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[...]

For Jules Feller, medieval Belgian authors were not trying to write in their local dialects (Wallon or Picard); rather, they were striving to write in French. However, because they did not have a perfect mastery of the central language, they attempted to deduce or "manufacture" French words by applying logical conversion rules or patterns of resemblance.

The creation of the word octembre is a perfect example of this phenomenon: [...] .

The dialects in question are Walloon and Picard. 

[...]

Very promising!, but of course now what about the 'b' in Aberil?
I once read that this could have been used in Luxemburg (which was quite a bit larger then), but I have not seen that appearing in discussions here.
Still interesting, as there would be a geographical overlap.