I reviewed the actual research instead of relying on reporters who compile text like this dailytech.com gibberish:
The team was able to come to these conclusions by digitizing and analyzing recordings of a 12-year-old male bottlenose dolphin from 1977. By doing this, they found that a dolphin breathes in a "heliox" mixture that consists of 80 percent helium and 20 percent oxygen. This combination would make humans sound like Donald Duck, according to the researchers, because it has a sound speed that is 1.74 times higher than normal air.The preceding quote gets many aspects of the research combined incorrectly and misstates the methodology of the study. Dolphins do not breath in "heliox," the researchers gave dolphins the helium mixture to test their sound making abilities underwater. It did not affect the sounds created by the dolphins which explains why dolphin noises do not change with depth.
What I found in the underlying research was astonishing. Several headlines announced that Dolphins were "talking." I concur that animals are much smarter and capable than we give them credit for, but the correct information is:
Rather than vocal cords, the dolphins likely use tissue vibrations in their nasal cavities to produce their “whistles,” which aren’t true whistles after all. The researchers suggest structures in the nasal cavity, called phonic lips, are responsible for the sound.The dolphins use these phonic lips in a similar fashion to humans. Additionally, dolphins possess communication and sonar-like abilities. The research did not go much further than that.
Dolphins have long been known to be intelligent but they lack many aspects that are important to human intellectual development. They do not have written repositories of information and likely do not have grandparents who can pass down learning while parents are busy.
To balance this downplay of dolphin capability, I must point to signs of impressive dolphin intelligence and communication. Namely, dolphins were trained to create new tricks on command and trained to do tricks in a group. When two star dolphins were given both commands together. The two dolphins submerged, communicated and then surfaced and performed a completely new trick in unison.
Further, dolphin language research details a simplified, short coded language that lacks many aspects of human language. It is similar to twitter with # and @ signifiers and limited in length. Scientists preliminarily call the dolphin language flipper and are partially decoding messages. The message closest to complete decoding, "(unknown), and thanks for all the fish."