decalitre, (kokuji)
竍 is a Japanese-made kokuji that represents the metric unit decalitre (ten litres). Its meaning is purely a measurement unit.
竍 is a modern kokuji created in Japan by combining 立 (standing) with 十 (ten) to represent the decalitre unit. It is not derived from classical Chinese character formation.
立 (stand) next to 十 (ten) suggests a unit of ten standing on its own: a decalitre.
For デカリットル, think of a decalitre as a 'deca-litre' — the reading is simply the katakana rendering of the English-derived unit name: デカリットル.