But if you go [and] learn a language against your will, then it's better not to go at all.

will 在这里是名词，意思是"意愿、意志"，指一个人内心真实的想法和决定。 against your will 是一个固定短语，表示"违背某人的意愿"，即做某件事不是出于自愿，而是被迫或勉强去做。