BOISE, Idaho — When the president of the Basques arrived here in Idaho’s capital from Europe late last month, the mayor stepped in to interpret for him into English from Basque, one of the world’s most ancient and difficult languages.

“Boise is part of Basque Country,” said the mayor, David H. Bieter, in an interview, explaining his role.

Mr. Bieter’s brother, John, a professor of history at Boise State University who was at the time running an academic conference across town about all things Basque — coordinated with the weeklong festival that had drawn the president, Iñigo Urkullu — said he could not agree more.

“If you’re into Basque studies,” he said, “this is Christmas.”

Many Americans might think of Idaho as potato country, so successfully has the agriculture industry branded the place, right down to the license plates. It is also one of the least ethnically diverse states, with more than 93 percent of its population classified as white, according to the census.