Coming from a game with alien technology of all kinds in the base game, energy weapons which melt people into goo, talking rats, armor which essentially turns a person into a walking tank when worn, radiation affects some people by making them immortal and turning them into ghouls, and a virus which turns people into giant, sterile green giants where most are dumb as rocks while others are far intelligent to any human, alongside one particular guy who fell into a vats of FEV goo and turned into the esker mutant blob from Aki... well, you get the idea...
Anyways, It strikes me as odd that 'talking-animals' are considered 'out-of-place' in the Fallout world where technological marvels and mutations with extreme effects on all beings are almost the norm. For one, most animals have been affected by radiation which has wild effects in this world, we also have the Enclave and other highly technological factions and areas in the wasteland. Their experiments and technology, alongside the effects of radiation and FEV could create a feasible explanation to how some creatures are able to gain higher intellect and the ability to communicate. Maybe some Enclave scientist escaped from Narravo with the data of their working with death-claws and was able to replicate the talking Death-claws once more. Either way, I played Fallout 2 last out of all the Fallout games and talking Deathclaws were not out-of-place to me in the slightest. It would ultimately depend on how it is handled, but it is possible and definitely not out of place in this universe.
To me anyways.
Anyhoo, I love the idea of a talking a Deathclaw companion, intelligent or not, I think it could be done in a lore-friendly way and would be pretty awesome to have a Deathclaw at your heel, giving some quip about the Wasteland or pointing out things in dumb, broken English.
That, and I want to marry it.