Question: Mennonites are traditionally multilingual with which Low Prussian dialect of East Low German, with Dutch influence language was their first?

Context paragraphs:
West Pomeranian dialect: West Pomeranian (German: "Westpommersch" or "Vorpommersch") is a dialect of the East Low German language and thus of the Low German language.  It is spoken today in West Pomerania ("Vorpommern") in northeast Germany.  Towards the west of the region it transitions gradually into Mecklenburgisch which, like West Pomeranian, belongs to the Mecklenburgisch-Vorpommersch dialect.  Towards the south it mixes with Brandenburgisch.  West Pomeranian has several West Slavic influences.  Characteristic is a hard, terse speech.

East Pomeranian dialect: East Pomeranian ("Ostpommersch") is an East Low German dialect that is or used to be spoken in Northern Poland (previously part of Germany until the end of World War II).  It is part of the Low German language.

East Low German: East Low German (German: "Ostniederdeutsche Dialekte" ) is a group of Low German dialects spoken in north-eastern Germany as well as by minorities in northern Poland.  Together with West Low German, it constitutes Low German.  Before 1945, the dialect was spoken along the entire German Baltic Coast, from Mecklenburg, through Pomerania, West Prussia into certain villages of the East Prussian Klaipėda Region.

Ostkäslausch: Ostkäslausch is a part of Low Prussian dialect of Low German spoken in an area of Poland, that used to be part of Germany.  It used to be or is spoken in Warmia in East Prussia.

Mundart des Ostgebietes: The Mundart des Ostgebiets is a subdialect of Low Prussian, a dialect of Low German.  It was spoken around Insterburg (now Chernyakhovsk, Russia), the Memel (Klaipėda, Lithuania), and Tilsit (Sovyetsk, Russia).  Many speakers of this subdialect were Prussian Lithuanians.

Low Prussian dialect: Low Prussian (German: "Niederpreußisch" ), sometimes known simply as Prussian ("Preußisch"), is a dialect of East Low German that developed in East Prussia.  Low Prussian was spoken in East and West Prussia and Danzig up to 1945.  It developed on a Baltic substrate through the influx of Dutch- and Low-German-speaking immigrants.  It overruled Old Prussian, which then became extinct in the 17th century.

Mundart des Weichselmündungsgebietes: The Mundart des Weichselmündungsgebietes (Vistula delta dialect) is a subdialect of Low Prussian, which belongs to East Low German.  The dialect was spoken in the region at the mouth of the Vistula River, around the city of Danzig (Gdańsk), Poland.

West Low German: West Low German, also known as Low Saxon (German: "Niedersächsisch" or German: "Westniederdeutsch" ; literally: "Nether-saxon"; Low German: "Nedersassisch, Nedersaksies, Platduuts, Plat(t)" ; Dutch: "Nedersaksisch" ; ) is a group of Low German (also Low Saxon; German: "Niederdeutsch" or "Plattdeutsch", Dutch: "Nederduits") dialects spoken in parts of the Netherlands, northwestern Germany and southern Denmark (in North Schleswig by the German minority).  It is one of two groups of mutually intelligible dialects, the other being East Low German dialects.

Plautdietsch language: Plautdietsch or Mennonite Low German, was originally a Low Prussian dialect of East Low German, with Dutch influence, that developed in the 16th and 17th centuries in the Vistula delta area of Royal Prussia.  The term "Plautdietsch" literally translates to 'Low German', "plaut" meaning 'flat' (referring to the plains of northern Germany), and the term "Dietsch" originally meaning "of the Tribe", and referring to all the continental West Germanic peoples and their languages (i.e. Low German, Dutch, High German).  In other Low German dialects, the word for Low German is usually realised as "Plattdütsch" or "Plattdütsk" , but the spelling "Plautdietsch" is used to refer specifically to the Vistula variant of the language.

Russian Mennonite: The Russian Mennonites (German: "Russlandmennoniten" occasionally Ukrainian Mennonites) are a group of Mennonites of German language, tradition and ethnicity, who are descendants of German-Dutch Anabaptists who settled for about 250 years in West Prussia and established colonies in the south west of the Russian Empire (present-day Ukraine) beginning in 1789.  Since the late 19th century, many of them have come to countries throughout the Western Hemisphere.  The rest were forcibly relocated, so that few of their descendants now live at the location of the original colonies.  Russian Mennonites are traditionally multilingual with Plautdietsch (Mennonite Low German) as their first language and lingua franca.  The term "Russian Mennonite" refers to the country where they resided after the split from Germany and not to their ethnic heritage.  In 2014 there are several hundred thousand Russian Mennonites: about 200,000 in Germany, 100,000 in Mexico, 70,000 in Bolivia, 40,000 in Paraguay, 10,000 in Belize and tens of thousands in Canada and the US and a few thousand in Argentina, Uruguay and Brazil.

Supporting paragraphs: Russian Mennonite Plautdietsch language
Answer: Plautdietsch