如果当年不贪玩英语可以用"If I had studied Engpsh more seriously back then"来表达。

这句话的来源是英语中使用的虚拟语气。虚拟语气表示假设的情况或事实，即“如果……就……”的意思。

例句：

If I had studied Engpsh more seriously back then, I would have a better command of the language now. (如果当年我认真学习英语，现在我的英语水平就会更好。)
If he had eaten more vegetables, he wouldn't have gotten sick. (如果他多吃了点蔬菜，就不会生病了。)
If she had left earper, she wouldn't have missed the train. (如果她早点走，就不会错过火车了。)

希望这些信息对你有帮助。