I think that rational thoughts are independent from language. Sometimes I have new ideas while sleeping and then have a problem to translate them into normal language and writing down after waking up.
Very often we get some visual information and its verbal description is also a problem. As we know, a digital image (for sequence even more) has more information than a sequence of words. Some of it is excessive, other (less important) details are never put into words. But if a sequence of images generates some abstract ideas, translation of them into words is even more difficult. That is why some creators prefer to paint a picture or to write music – in this manner a lower fraction of their ideas will be lost
Hence; rational thought exist without language but those can not be communicated without a language. There need a language to communicate your thoughts.