With telepathy or direct neural links, there's little need for a language
Language is a form of communication. It is required in the first place because ideas can not be transmitted directly between the individuals. But what if they could? What if one individual can easily communicate an idea of "big red tasty fruit" to others, do these individuals ever develop words for "big", "red" "tasty" or "fruit"? As long as this "idea exchange" is reliable, no intermediary language is necessary, it would only slow the communication down.
The lack of written language would impede any technological development. Without an ability to confine ideas to some sort of medium knowledge cannot be effectively preserved or distributed. Here we probably have to do more handwaving and introduce a kind of medium where ideas can "written" and "read" - all without a need for language.
Next hurdle would be to invent "machine language". In XIX century people already had a need to make up some form of instructions that was supposed to be read by some mechanism, for example Jacquard machines or music boxes. In XX century these machine languages became indispensable. We can continue our handwaing and say that in this civilization primitive machines can read ideas too, however I think this would be definitely in the realm of magic.
Overall it seems very plausible that a civilization of telepaths can reach XVIII century level of technology without the need to develop any language.