先来看一下joinder及joinder agreement的含义：

Joinder：the action of bringing parties together; union.

Joinder Agreement: An agreement joining a person as party to another agreement as if such person was an original party to such agreement. Joinder agreements are commonly used when new stockholders or LLC members receive equity and are made party to an existing stockholders' agreement or LLC agreement.

由上可知，joinder agreement的作用其实就是将某人添加至某一协议的缔约方，使其如同协议原始缔约方般受协议约束。

因而，从这一点来看，可以直接将其译为“加入协议”，或者也可以将其译为“联合协议”，取联合关于“结合在一起”这一层含义。

以下为某股份购买协议后附joinder agreement双语条款，供参考：

JOINDER AGREEMENT

The undersigned is executing and delivering this Joinder Agreement dated [*] pursuant to the Share Purchase Agreement, dated as of [*], 202[ ] (the "Purchase Agreement"), by and among (i) AAA, an exempted company duly incorporated and validly existing in the Cayman Islands, (ii) [ ], a limited liability company established under the Laws of [ ]; and (iii) the parties listed on Schedule A-1 of the Purchase Agreement.

Capitalized terms used but not defined in this Joinder Agreement shall have their meanings in the Purchase Agreement.

The undersigned hereby acknowledges, agrees and confirms that, by its execution of this Joinder Agreement, it shall be deemed to be a Party to the Purchase Agreement as of the date hereof and shall have all of the rights and obligations of the "Investor" thereunder, as the case may be, as if it had executed the Purchase Agreement.

The undersigned hereby ratifies, as of the date hereof, and agrees to be bound by, all of the terms, provisions and conditions contained in the Purchase Agreement.

IN WITNESS WHEREOF, the undersigned has caused this Joinder Agreement to be duly executed and delivered as of the date first written above.

[*]

By: _______________________

Name:

Title:

联合协议

下列签署人于202【】年【   】根据202【】年【   】的《股份购买协议》（“购股协议”）签署并交付本《联合协议》，签署方为 (i) AAA，一家在开曼群岛正式注册成立并有效存续的豁免公司，(ii)【 】，一家依照【 】法律成立的有限责任公司；(iii) 购股协议附表 A-1 所列各方。

本联合协议中使用但未定义的术语的定义见购股协议。

下列签署人在此承认、同意并确认，通过签署本《联合协议》，自本协议签署之日起，其将被视为购股协议的一方，并享有购股协议项下“投资者”的所有权利和义务（视情况而定），如同其已经签署了购股协议一样。

自本协议签署之日起，下列签署人在此批准并同意受购股协议中所有条款、规定和条件的约束。 

下列签署人已使本《联合协议》于文首所载日期正式签署并交付，以昭信守。

【*】

签字：_______________________

姓名：

职务：