Is French word fiancailles translated in Hebrew as Erabon?

No. No no no.

The Hebrew word ’erabon “pledge” (Strong 6162. עֲרָבוֹן (erabon)) shows up in Greek as arrabōn. In fact, it doesn’t quite: the word was borrowed in Classical times, so it was likely taken from Phoenecian instead.

Within Greek, arrabōn ended up meaning “engagement, betrothal”, because a betrothal is a kind of pledge. But that change is no earlier than Athanasius of Alexandria (according to Lampe), which makes it 700 years after the word is first attested in Greek. And it has nothing to do with Hebrew. Therefore, עֲרָבוֹן cannot be translated as “fiancailles”.