You will need two weeks for Baltic languages alone

)
And if you manage to fix whether Curonians were East or West Balts...
Whether Lettigalians indeed deserve their own culture or should be part of East Baltic common group in early start dates.
(Latvians should possibly be melting pot between East Baltic, West Baltic, Uralic under German superstrate).
Also good luck reconstructing fonetics of Uralic languages and relevant melting pots. If you do it in 2 weeks generations of linguists would thank you
In meantime you could also establish location of East Galindians and their fonetics (got extinct after 1000 AD, somewhere near modern Moscow) and ensure their namelist for all melting combinations.
Well, I was figuring that a reasonable line to draw would be at the limits of the modern scholarly consensus. But then I guess that isn't being totally "right" in away similar to how Asbjorn di Canossa wouldn't be right... but it's as right as we can get within the bounds of modern knowledge.
So, at the risk of sounding hypocritical/arbitrary, we'd just make (as highly as possible) educated guesses as to the phonology of underdocumented/reconstructed languages, and/or assume for our purposes that they are identical to better documented relatives. It'll be right enough!
But once you have your inventories of phonological systems, it shouldn't be too hard. You then need a script that picks the best match-ups between phones in either language, and also applies changes to respect differences in phonotactics. The real bitch would be turning the IPA forms into each language's orthography, which means making a database of each orthography, and writing rules to turn IPA forms into that orthography. In less-phonemic orthographies, you'll just have to pick one grapheme or so for each phoneme.
But... after all that, I think you'd end up with a system that most linguists would consider good enough for a videogame. And that's the highest standard you can hope for, I think.
EDIT:
To demonstrate an example (half-assing the IPA):
Old Norse > Italian melting pot
Transfer 10 Old Norse names to Italian name pool
Asbjorn Arnbjörn Hroðgar Ingjald Kettilmund Olafr_Olaf Snorri Þorbjörn Öysteinn
/asbjorn/ /arnbjɔrn/ /hroðgar/ /ingjald/ /kettilmund/ /olavɾ/ /snori/ /θorbjorn/ /œystein/
Apply Italian phonotactics (and delete some? all? grammatical endings)
/asbjorno/ /arnebjɔrno/ /hroðegaro/ /ingjaldo/ /kettilmundo/ /olavo/ /snori/ /θorbjorno/ /œysteino/
Apply Italian phonology
/asbjorno/ /arnebjɔrno/ /rodegaro/ /ingjaldo/ /kettilmundo/ /olavo/ /snori/ /torbjorno/ /eisteino/
Apply Italian orthography
Asbiorno Arnebiorno Rodegaro Inghialdo Chettilmundo Olavo Snorri Torbiorno Eisteino
Aaaaand I notice there's a whole lot of other stuff you'd have to do. Preferred epenthetic vowels by language, how to represent grammatical endings like -r that are often lost in borrowing, how each language fits loans into their own grammatical system (I picked -o as the ending because most earlier Germanic loan names ended in it)...
OK, make it a month of work.