Probably first referred to the two shilling coin, also known as the florin, which had four crowned cruciform shields with a rose in the centre. It was later used for the Dutch guilder, which replaced an older currency known as the florin. Since the guilder was used in Indonesia, when the rupiah replaced it, the Chinese name for the guilder continued to be used for the rupia

Kroonen, Guus (2013) Etymological Dictionary of Proto-Germanic, Leiden, Boston: Brill, page 442.

from Proto-Germanic *skildlingaz from *skelduz 'shield' +‎ *-lingaz '-ling'

Old English sċilling, Middle English shilling, Scots schilling, English shilling, Old Frisian skilling, Old Saxon skilling, Middle Low German schillink, Middle Dutch schillinc, Dutch schelling, Middle High German schillinc, German Schilling, Old Norse skillingr, Icelandic skildingur, Faroese skillingur, Old Swedish skillinger, Swedish skilling, Danish skilling, Norwegian skilling, Gothic skilliggs

Alternative reconstruction: *skellingaz from *skiljaną 'to cut; to split, divide; to separate' +‎ *-lingaz (Orel, Vladimir (2003) A Handbook of Germanic Etymology, Leiden: Brill, page 338)