一天到晚A修饰B，B修饰C，C修饰D

偶尔也忍不住手痒，写下几句英文，呵呵

Ngram Viewer can always tell us something.

Ngram shows the phrase, game for a laugh, came into use as early as in the 1960s, but it was not widely used until about 1985, when, as we know, a British light entertainment program of the same name began to run. The series show, as do those entertainment programs currently put on the air in our country, was mainly revolved around all sorts of practical jokes.

Now let's come back to the two translated versions.

a. 他总是笑口常开。——大概说他性格乐观。

b. 他总是愿意找点乐子。——大概说他热爱生活，有情趣。

Which one is better? It's hard to tell. 

It seems to me neither of them fits the original meaning of the phrase. As far as I know, a participant who is brought in such a program or in the game is usually not aware of his or her being played pranks on or something like that, until the episode of the program that they are involved in comes to an end. The victim is then called "game for a laugh". An example for the phrase goes like this, “So if you are game for a laugh and you want to challenge your brain, give one of these a go!”That sounds fine and is exactly the way I use it.

A Chinese phrase or sentence can always, if you mean to, be so sinuous, convoluted as to help you win access to what you want to mean.  It just a matter of imagination. 

That said, b maybe good for some people.

   game adj. 1.willing or ready to do something 愿意（或准备）去做的...... They were game for anything. = They were game to try anything. 他们愿意尝试任何事情。（摘自《韦氏高阶英汉双解词典》）

  【1】He's always game for a laugh.   他总是笑口常开。

                    《朗文当代高级英语辞典（英英·英汉双解）（第4版）》

  【2】He's always game for a laugh.  他总是愿意找点乐子。

                     《朗文当代高级英语辞典（英英·英汉双解）（第5版）》

    后一种翻译更合理。

adjective 

  willing to do things that are new, risky or difficult 

      • It was a difficult challenge, but Roberta was game. 

      • She's game for anything.