Going from Persian (Farsi) to Yiddish (ייִדיש) has a composite linguistic distance of 78% (heuristic estimate). Below is the dimension-by-dimension breakdown.
Shared vocabulary, cognates, and loanwords.
Morphology, syntax, word order, cases.
Shared sounds and phoneme inventory.
Arabic → Hebrew
Indo-European ↔ Indo-European
The 5 languages with the lowest linguistic distance from Persian (Farsi):
A quick 3-question check between Persian (Farsi) and Yiddish. No signup.