I think it rather depends on how you define language. For example, Wikipedia says the following:

Depending on philosophical perspectives regarding the definition of language and meaning, when used as a general concept, "language" may refer to the cognitive ability to learn and use systems of complex communication, or to describe the set of rules that makes up these systems, or the set of utterances that can be produced from those rules.

What kind system of complex communication do we have in DNA/RNA? It sure is a mode of storing and transferring information. But does this make it a language? And if yes, who is speaking the language of DNA/RNA? Can cells talk then? Because I would argue that this (hypothetical) language of DNA is then always "spoken" by individual cells and isn't transferrable to a multicellular entity? (I mean, sure all your cells are "speaking" DNA in this way, but you yourself aren't.) But back to the question of the "complex systems of communication". I would argue that while DNA is a mode of transferring information, it isn't a language in itself. Because you don't have a back-and-forth. It is a pretty simple progression of reusing information again and again. But it isn't a mode of communication and especially not complex communication.