Going from Belarusian to Irish (Gaeilge) has a composite linguistic distance of 71% (heuristic estimate). Below is the dimension-by-dimension breakdown.
Shared vocabulary, cognates, and loanwords.
Morphology, syntax, word order, cases.
Shared sounds and phoneme inventory.
Cyrillic → Latin
Indo-European ↔ Indo-European
The 5 languages with the lowest linguistic distance from Belarusian:
A quick 3-question check between Belarusian and Irish. No signup.