“双方另行协商”可直接译为“both parties shall negotiate”，而不加 “separately”。

如：本合约未尽事宜，双方另行协商，签订补充协议。

Other miscellaneous items uncovered in this agreement will be negotiated by both parties and sign appendix agreement.  

“separately”在法律文本指“单独地；分割地；不想联地”，通常相对于“jointly”。

如：

Observer organizations show continued interest in intersessional workshop participation having made, separately and jointly, 170 substantive submissions in 2011.

观察员组织继续对参与闭会期间的研讨会表示兴趣，2011 年，它们单独或联合提交了170 份实质材料。 

All such communications to and from the appointing authority and the Secretary-General of the PCA shall jointly or separately also be provided by the sender to all other parties. 

一方当事人与指定机构和常设仲裁院秘书长之间的所有此种函件也应由发 件人联合或单独提供给 其他各方当事人。 

另，关于 separately 和 jointly，在填写婚姻状况的时候也有相关的一组词：

Married filing jointly (MFJ): To file jointly means you file a single return, which will include the income and deductions for both spouses.

Married filing separately (MFS): Each person files their own return, keeping incomes and deductions separate.