At 26 months he is not potty delayed. In my experience, most boys do not potty train until they are three years old. I have known many parents who start training their boys at the age of two, but take an entire year of potty training before the child is trained. I have also known many parents who waited until their sons turned three and potty trained in a few days. There are of course a few who will tell you that their son was fully trained and independent on the potty at two or younger, but that is not usual. My advice would be to put the potty training on hold until his third birthday (or until he shows interest in training) and concentrate on his speech.
ETA: I have two boys who both potty trained as soon as they turned three. One was very advanced in his speech and the other was a late talker.
ETA: Sorry, I guess I misunderstood. I thought you were saying he was both potty and speech delayed. Sign language is a good suggestion. Both of my boys took a sign course with me when they were about 18 months. They learned many signs, but they didn't potty train any sooner.
Also, we didn't "throw out the diaper and do it in a week." If you wait until the kid is actually ready it only takes a few days. Why waste six months training them to do something that will come naturally to them in a few days if you just wait?