While a few countries are identified by name in the story "Running of the Bulls", a science fiction parody of Ernest Hemingway's The Sun Also Rises, Harry Turtledove only provides enough detail about those countries to make clear which OTL countries they are analogs of. Therefore, much of this article is not written "in-universe".
Astilians worship the bull-god Thimras (anagram of Mithras). The Skeuaran people reside within Astilia's borders, and speak a very old and difficult-to-learn language. (These are analogous to the Basques; the native name for their language is Euskera or Euskara).
Amblona is an analog of Pamplona, Spain.
Ganelon was a small town in Northern Astilia. Baek Jarns and Obert Ohn stopped there to fish for a time on their way to Amblona. Ohn left Jarns in Ganelon so he could meet with Ett Brashli. Jarns was not offended, and continued to fish on his own for a time.
Ganelon was the site of a medieval battle. Two armies fought until one triumphed. There had been a famous epic poem, ensuring that next to nobody had ever heard of Ganelon, rather than nobody having ever heard of it.
Ganelon is a stand in for Burguete, the town Jake Barnes stops to fish in in The Sun Also Rises. However, Ganelon is the name of a knight who betrayed Charlemagne in The Matter of France.
Dubyook is an analog of the United States of America. It is a young country, located on the other side of an ocean from Ecnarf. The most common language is Dunlinese, but there are subtle differences between the dialects spoken in Dubyook and Dunlin. Baek Jarns and Obert Ohn hail from Dubyook, both having fought during a substantial global conflict, and then opting to remain in Ecnarf rather than return home.
The significance of the name "Dubyook" is unclear, as it does not contain any obvious wordplay on either "United States" or "America".
Although "dunlin" is a small bird native to the UK among other countries, the name in this context appears to be a phonetic anagram of London, the capital of the UK.
Ecnarf is an analog of France. The name "Ecnarf" is "France" spelled backwards. Ecnarf's geography uses the same naming rule. Ecnarf is separated from Astilia by a mountain range which is reportedly tyr-infested.