Ilona being the Hungarian version of Helen is not a "possibly thing", it's a fact. It's even said on Wikipedia. It came to Hungary from Slavic countries. It comes from Jelena.
― Anonymous User 12/15/2021
2
https://hu.wikipedia.org/wiki/Ilona -- They consider this name a medieval Hungarian corruption of Jelena, claiming the evolution to have been "Jelena → Jelona → Ilona".
― Anonymous User 11/19/2020
3
'Ilona' literally means 'to be a joy to someone/something' in finnish.
Derivative from finnish word "ilo" menaning joy. Also Ilona is the noun ilo conjugated such as "she exists for our joy", so the person is for example presently "joy" for the passive voice.