“定为货币”常见的英文表达可以是 “be designated as currency” 或 “be established as currency”。
“designate” 有“指定、选定、命名”之意，“be designated as currency” 即表示“被指定为货币” 。
“establish” 意思是“确立、确定、建立”，“be established as currency” 可理解为“被确立为货币” 。
例如：This particular metal was designated as currency in that ancient kingdom.（在那个古老的王国，这种特定的金属被定为货币 。 ）