Is it possible for FrancoProvencal and Piedmontese to lose individuality and merge into a single language and what POD is needed for that.
It is Arpitan not Catalan/Provencal merging with Piedmontese...With a medieval PoD you could easily accomplish this. The two dialects/languages have more in common with each other than they do with either modern French or Italian.
You essentially need to do two things: Keep Provence from being absorbed by France (presumably involving political union with northwestern Italy), and keep the resulting state from deciding it's Italian and taking over the Peninsula.
Provence was only an integral part of France from 1486. If you can both weaken or distract France and provide Piemontese e Provencal union in the 13th-15th century window you are essentially there.
Much further down the road, Italian nationalism would be a very real question. Either Italy would not form at all, or would share the peninsula with Provence-Piedmont.
I asked this question because the Arpitan and Piedmontese speakers are found on Piedmont-Sardinia.The issue with this, to my mind, is that it's really difficult to define what a language is. I mean, they could theoretically be treated as one language with different dialects, it really depends on the political/academic situation. This becomes even tricker with the two langauges you give as examples because they're part of the Italo-Western dialect continuum where determining language is fairly difficult. I mean, I'm not an expert on this, but i would bet that if you traveled to near the "border" of Franco-Provencal and Piedmontese in the era before national language replaced much of their usage, you'd be hard pressed to determine where one language begins and where stops.
So, to do this, to have the two languages treated as one languages in an ATL, the easiest thing to do would probably be to have on of the transition dialects accepted as some kind of standard, or have both of them in one polity so that