Question: Which language closely related to the Frisian languages does Robin D. Gill speak fluently?

Context articles: Kashubians
Magori language
Frisian literature
Phu Thai language
Minahasan people
Frisian languages
Arapaho
Robin D. Gill
English language
Saterland Frisian language

Kashubs (Kashubian: "Kaszëbi" ; Polish: "Kaszubi" ; German: "Kaschuben" ) also spelled as Kaszubians, Kassubians, Cassubians, Cashubes or Kashubians, and formerly known as Kashubes, are a West Slavic ethnic group in Pomerelia, north-central Poland.
 Their settlement area is referred to as Kashubia (Kashubian: "Kaszëbë" , Polish: "Kaszuby" , German: "Kaschubei, Kaschubien" ).
 They speak the Kashubian language, classified either as a separate language closely related to Polish, or a Polish dialect.
 In analogy to the linguistic classification, Kashubians are considered either an ethnic or a linguistic group.
 Kashubians are closely related to Poles.
Magori is a nearly extinct Austronesian language of Papua New Guinea that has been strongly restructured through contact with neighboring Papuan languages, perhaps Mailu, which the Magori people speak fluently today.
 The restructuring was so extensive that Magori's family was long in doubt; it was finally established by Dutton in 1976.
 Magi in turn borrowed large numbers of Austronesian words, either from Magori or its extinct Oumic relatives.
Frisian literature is works written in the Frisian languages, particularly that of West Frisian spoken in the province of Friesland in the Netherlands, from which most texts were produced or have survived.
 The first texts written in Frisian emerge around the 13th century.
 Frisian as a written language has for the most part historically been secondary to Dutch and Latin for all official purposes.
Phu Thai (Phuu Thai; Thai, Phu Thai: "Phasa Phuthai", ภาษาผู้ไท or ภูไท) is a Thai language closely related to Tai Dam and Tai Dón, it is less closely related to the Isan and the Lao languages.
 It may be the same as Tay Khang.
The Minahasans (alternative spelling: Minahassa or Mina hasa) are an ethnic group located in the North Sulawesi province of Indonesia, formerly known as North Celebes.
 The Minahasa people would refer to themselves as Kawanua people, Touwenang people or more commonly as Manado people.
 They are actually a nation with oldest democracy and federal nation in the middle of the other Indonesian Tribes, even in Asia, because of their old tribal united government (declared in ).
 They are the most populous ethnic group in the Minahassa Peninsula.
 They are a Christian-majority ethnic in a country (Indonesia) with a Muslim majority.
 The Minahasans speak Minahasan languages as sub-tribal language for every sub-tribe of Minahasa and Manado Malay (also known as "Minahasa Malay"), a language closely related to the Malay language as national language in the local area.
The Frisian languages are a closely related group of Germanic languages, spoken by about 500,000 Frisian people, who live on the southern fringes of the North Sea in the Netherlands and Germany.
 The Frisian languages are the closest living language group to the Anglic languages; the two groups make up the Anglo-Frisian languages group.
 However, modern English and Frisian are not mutually intelligible, nor are Frisian languages intelligible among themselves, due to independent linguistic innovations and foreign influences.
The Arapaho ( ; in French: "Arapahos, Gens de Vache") are a tribe of Native Americans historically living on the plains of Colorado and Wyoming.
 They were close allies of the Cheyenne tribe and loosely aligned with the Lakota and Dakota.
 The Arapaho language, "Heenetiit", is an Algonquian language closely related to Gros Ventre (Ahe/A'ananin), whose people are considered to have separated from the Arapaho at an early time.
 The Blackfeet and Cheyenne also speak Algonquian languages, but theirs are quite different from Arapaho.
Robin Dallas Gill, born in 1951 at Miami Beach, Florida, USA, and brought up on the island of Key Biscayne in the Florida Keys, is a bilingual author in Japanese and English.
 He wrote extensively on stereotypes of Japanese identity before moving on to publishing his research on, and translations of Japanese poetry, especially the genres of haiku and senryū.
 He is considered a 'maverick' writer within the field of Western studies on Edo-period poetry.
 He writes haiku in Japanese under the "haigō" (haikai pen-name) Keigu (敬愚:'Yours foolishly', an homophonous pun on 敬具:'Yours truly').
 Since 2013, he has been engaged in writing in Japanese for a Japanese audience, hoping to help, via introductions to the comic traditions of Japanese poetry, to shake Japan out of its "cultural doldrums".
 Much of his output has, according to Gill's own testimony, been done while a pauper for much of his life.
English is a West Germanic language that was first spoken in early medieval England and is now a global "lingua franca".
 Named after the Angles, one of the Germanic tribes that migrated to England, it ultimately derives its name from the Anglia (Angeln) peninsula in the Baltic Sea.
 It is closely related to the Frisian languages, but its vocabulary has been significantly influenced by other Germanic languages, particularly Norse (a North Germanic language), as well as by Latin and Romance languages, particularly French.
Saterland Frisian, also known as Sater Frisian or Saterlandic ("Seeltersk"), is the last living dialect of the East Frisian language.
 It is closely related to the other Frisian languages—North Frisian, which, like Saterland Frisian, is spoken in Germany, and West Frisian, which is spoken in the Netherlands.