“订立合同”常见的英文表达是 “enter into a contract” 或 “conclude a contract” 。
enter into a contract：侧重于描述开始或达成进入合同关系这一行为过程 ，强调进入合同关系的动作。例如：Both parties agreed to enter into a contract for the supply of goods.（双方同意就货物供应订立合同。）
conclude a contract：更强调合同最终达成、签订这一结果，有完成、结束谈判并订立合同的含义。例如：After several rounds of negotiations, they finally concluded a contract.（经过几轮谈判，他们最终订立了合同。 ）