Definitely recommend taking the time to read or at least skim the article, and not react to headlines, because headlines are so often over-simplified and even click-baity.
Species of animals do appear to have natural regional differences. And maybe regional differences in humans or human languages affect animals too, who knows? There's a slim chance that animals from different countries might not understand each other because countries are a human concept.
https://drsophiayin.com/wp-content/uploads/2015/04/Yin2004Ba...
Some less-dense coverage:
https://www.star2.com/living/2018/02/27/ev-when-your-dog-bar...
"All the people were pretty good at figuring out what was going on. There were no significant differences between dog owners and non-dog owners. They were particularly good at identifying dog emotion in Stranger Danger, Guard Dog, Alone, and Play."
These are interesting studies, but many nevertheless wonder why scientists bother. Most of us understand a common language for terrestrial animals. Lower-pitched sounds come from bigger animals with bigger throats. I've never been growled at by a lion, but I would understand that a deep low growl means it is trying to scare me with its size. This holds true for bears, dogs, cats, deer, even humans. Conversely, high-pitched screams are generally calls for help, mimicking the pitch of the young. Showing your teeth is a near-universal sign of aggression. Put this all together and it is enough to satisfy most definitions of language.
On topic, I have a parrot that can call the dogs name, the dog comes running and the bird throws food at him...then laughs. Sometimes in a British accent. I am not sure where he picked that up.
The question isn't really whether they 'understand' each other, but whether the differences cause changes in behaviour. Some birds preferentially mate with others that sound most like themselves. Others, because nature is complicated, do the opposite.
[0] https://web.stanford.edu/group/stanfordbirds/text/essays/Voc...
