Here’s some of the etymology of orange from www.etymonline.com:
c.1300, from O.Fr. orenge (12c.), from M.L. pomum de orenge, from It. arancia, originally narancia (Venetian naranza), alt. of Arabic naranj, from Pers. narang, from Skt. naranga-s “orange tree,” of uncertain origin. Loss of initial n- probably due to confusion with definite article (e.g. une narange, una narancia), but perhaps infl. by Fr. or “gold.” The tree’s original range probably was northern India. The Persian orange, grown widely in southern Europe after its introduction in Italy 11c., was bitter; sweet oranges were brought to Europe 15c. from India by Portuguese traders and quickly displaced the bitter variety, but only Mod.Gk. still seems to distinguish the bitter (nerantzi) from the sweet (portokali “Portuguese”) orange.
To summarise, it started off with an initial n- which got lost in Italian and French. But compare these with some other Mediterranean languages:
Italian: arancia (-cia is a palatal fricative, pronounced -tcha)
French: orange (ge sounds like the -s- in measure, a retroflex sibilant)
Spanish: naranja (j is a velar fricative, rather like German Bach)
Portuguese: laranja (j like the French ge)
Catalan: taronja (j like English jam)
(Rather confusingly, Portuguese toranja is a grapefruit)
So we have four different initial sounds (n, l, t and null). German has Apfelsine (Apfel = apple), but mostly uses Orange- in compounds such as Orangensaft (orange juice).
Brits have marmelade on their breakfast toast, where marmelade refers to jam made from any citrus fruit, but by default oranges. Yet the word comes straight from Portuguese marmelada from marmelo – quince. So I assume somebody a long time ago tried using oranges instead of quince and the idea was a hit. (In Spain, mermelada is any sort of jam and quince is membrillo.)
Once you start looking at words, one thing just leads to another…