Which plaintext languages to try?

[nablator]

E.g., I have trouble understanding the parts I circled below, what do these abbreviations stand for?

7: ch with macron: not Latin. Maybe Italian-specific?
13: quod
14: quam

As far as I have seen, mostly people are referred to Cappelli for the scribal abbreviations, but there are probably hundreds of abbreviations in Cappelli's book

Thousands.

I'm mostly looking for a list of 5-10 most popular ones, like -9 for -us.

I don't have statistics (they vary a lot with time, origin and scribe) but I guess some of the most common Latin abbreviations of the 15th century are:
- vowels with macron omitting the following n/m
- apostrophe for er/re
- a small tilda (~) for -ur
- "2/" for -rum
- small 9 for -us (also -ost) and a bigger 9 for con/com (sometimes the same size).
- quod, que, quem, quam, qui...
- per/par/por, pre, pro...
- et

Is this list reasonable?

Looks good. No idea if Occitan and Provençal were more or less written than some German, Italian, Spanish dialects.

What about Greek and Arabic, were they used in parts of Europe at that time?

Last time I checked Greece is/was in Europe.

Not much remained of Al-Andalus until the 15th century, in the south of Spain.

Could someone suggest a good resource to find samples of each of these language variants, preferably both transcribed and as a photo? I think a short text of about 50 words for each of the languages will be enough, I'm just interested in basic statistics.

Some datasets were shared by researchers, incomplete and of variable quality. I'm not sure if I should recommend any of them.