I not only can speak English, but also I can speak French.
这句话是不是对?
not only...but also...前后引导的结构是不是要对称?譬如将本句改为:I not only can speak English, but also can speak French.
你的句子是错误句子。应该改为:I can speak not only English but also French. 虽然说not only, but also 在有的情形下可以不对称,如倒装,Not only 放句首等状况,但通常情况下是要维持对称,降低重复。