A few pages that list etymologies have orange being from Sanskrit "naga ranga", meaning "fatal indigestion for elephants". The story goes that there is an ancient Malay fable of an elephant dying from eating an orange. This seems to me to be a great story, but false.
orange is from Sanskrit, specifically from Old French pume orenge, from Old Italian melarancio from mela "fruit" + arancio "orange tree", which is from Arabic nāranj, from Persian nārang, from Sanskrit नारङ्ग nāraṅga "orange tree". The trail ends there, altho the AHD says "possibly of Dravidian origin." There are some Dravidian words that could be the source: Tamil நாரம் nāram "orange", நாரங்கம் nāraṅkam "bitter orange tree"; Telugu నారింజ nāriñja "bitter kind of orange", నారంగము nāraṅgamu "orange tree", నారదము nāradamu "a sort of orange", నారిం nāriṇẓa "orange"; Tulu ಣಾರೆಂಗಿ nāreṅgi. The Multilingual Plant Name Database has Malayalam narakam and Kannada naranga. Some of these might be borrowed from Sanskrit.
But "fatal indigestion for elephants" seems very fanciful, and not supported by these Sanskrit dictionaries. नाग nāga does mean "relating to serpents or elephants", but रङ्ग raṅga is "colour, hue; theatre, play-house, stage, arena" and राङ्ग rāṅga is "actor". Are oranges really poisonous to elephants?
The name of the French town of Orange is unrelated; it comes from Latin Arausio from Celtic.