What are the regional languages in Germany besides High German, and where exactly are they spoken?

Bavarian and Swabian are just dialects. Germany is home to five officially recognized regional languages that are entirely distinct—including a Slavic tongue and English's closest relative.

Low German (Plattdeutsch)
Spoken across the northern third of Germany—including Lower Saxony, Schleswig-Holstein, Bremen, Hamburg, Mecklenburg-Vorpommern, and parts of North Rhine-Westphalia and Brandenburg—Low German is the most widespread regional language. It never underwent the High German consonant shift, meaning it sounds closer to Dutch and English than to standard German. For instance, the Low German word for "water" is Water, and "to make" is maken, aligning perfectly with their English and Dutch counterparts rather than the High German Wasser and machen.

Frisian
Frisian is spoken in two distinct pockets and is the Germanic language most closely related to English. North Frisian is spoken on the west coast of Schleswig-Holstein and its adjacent North Sea islands, like Sylt and Föhr. Saterland Frisian, a remnant of East Frisian, survives in a single municipality in Lower Saxony.

Sorbian
Deep in eastern Germany near the borders of Poland and the Czech Republic lies the region of Lusatia. Here, a minority population speaks Sorbian, which is not a Germanic language at all, but a West Slavic one related to Polish and Czech. Upper Sorbian is spoken in the state of Saxony around the city of Bautzen, while Lower Sorbian is spoken further north in Brandenburg around Cottbus.

A place-name sign on the outskirts of Bautzen displaying the city's name in both German and Upper Sorbian. Source: Wikimedia Commons.

Danish
Danish is an officially recognized minority language in the northernmost state of Schleswig-Holstein, specifically in the region of Southern Schleswig just south of the Danish border. The Danish minority operates its own network of schools, libraries, and churches in the area.

Romani
Unlike the others, Romani has no specific geographic concentration. It is the language of the Sinti and Roma people, who have lived in German-speaking territories since the early 15th century. It is recognized as a minority language nationwide under the European Charter for Regional or Minority Languages.