You say Groundhog Day, I say Grundsaudaag: how German and Swiss settlers in Pennsylvania created a new language – and a much-loved American holiday.

Every 2 February since at least 1886, people have been gathering in the Pennsylvanian town of Punxsutawney to watch a groundhog – a furry rodent – crawl out of a hole after its winter sleep. If the day is sunny and the groundhog sees its own shadow, there will be six more weeks of cold weather, according to legend – but if it's a cloudy day, and there is no shadow, spring has arrived. Across the US, the quirky tradition is known as Groundhog Day. But among its original celebrants, it has a different name: Grundsaudaag.

At first glance, Grundsaudaag may look like an ancient German word. Instead, it is actually an example of Pennsylvania Dutch, a Germanic language that emerged in the 18th Century and is now mostly used by the Amish and Mennonite religious communities. Due to the rapid growth of the Amish population, which numbers almost 380,000 people and for whom the language has a special spiritual and cultural significance, this relatively little-known language is in fact thriving and growing.

So what exactly is Pennsylvania Dutch? And how is it linked to Groundhog Day?

"As a linguist and language enthusiast, I love all languages. But there is something special about the language of my heritage, the one spoken to me when I was a child," says Rose Fisher, a PhD candidate in German linguistics and language science at the Pennsylvania State University.

Fisher grew up in the Amish community in Lancaster County, Pennsylvania. Her family left the community when she was 11, and now mostly uses English, she says. Even so, she adds, "I love to hear Pennsylvania Dutch being spoken around me and hope that someday I will be around it more, and more comfortable speaking it again. For me, it means I am home." She and her family still use certain Pennsylvania Dutch words when speaking English "because they refer to concepts that do not exist in the English-speaking world. One that comes to mind is 'gluschdich' which means 'I am not hungry but I feel like eating!'"

Historically, the "Dutch" part of Pennsylvania Dutch referred to various Germanic languages in Central and Western Europe, including German, says Mark Louden, a professor of Germanic linguistics at the University of Wisconsin-Madison and the author of Pennsylvania Dutch: The Story of an American Language.

"Pennsylvania Dutch has always been a hybrid language," he says, adding that like the American culture it is part of, it incorporates influences from a variety of sources.

In the 18th Century, over the space of several decades, a group of around 81,000 people moved to America from the conflict-ravaged German region of the Palatinate (Pfalz in German), Louden says. Among them were a few hundred followers of Jakob Ammann, a Swiss religious leader. They had left Switzerland and settled in Alsace and Palatinate, but were now on the move again – to Pennsylvania, a religiously tolerant colony, where they would become known as the Amish.

In the 1780s, Louden says, the first historical descriptions appeared of "a very

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