Can my dog understand a French dog, or do they bark in a different language?
Yes. Animals from different places do sound different (there is research showing the birds and cows have ‘accents’) but a lot of the dog’s communication is non-verbal, scents and body language. Similar to how humans can communicate with someone from elsewhere by facial expression and gesture I guess, and probably how we did it before language. A dog’s communication doesn’t respect national boundaries like a human’s does.
You can understand if a British dog is happy, sad, pleased, angry, whatever and you can tell the same for a a French one. Other dogs will be getting a lot of nuance we aren’t picking up of course.