The language native to Spain with the fewest speakers is Quinqui, spoken by the Mercheros in Northern Spain.
It is difficult to determine the least common language spoken in the world due to limited data and the vast number of languages. However, some of the least spoken languages include endangered indigenous languages with only a few remaining speakers.
klingon
Ainugo
One of the least spoken second languages worldwide is Luxembourgish, which is primarily spoken in Luxembourg. It has around 400,000 speakers and is predominantly used as a second language alongside French and German.
The least spoken language in India is usually considered to be the Nihali language, spoken by a small number of people in the Maharashtra region. It is a severely endangered language with very few speakers left.
english
The Basque language, spoken in the Basque Country in northern Spain and southwestern France, is considered least influenced by the Indo-European migrations. It is a language isolate, meaning it has no known relatives, and its origin and structure are not related to the Indo-European language family.
The least would be either Lao (From Laos), Dhivehi(from the Maldives Islands), Kazakh (Kazakhstan) or Uzbek (Uzbekistan), spoken by less than 10 people in Mexico, all of them registered immigrants.If you mean the least spoken, native language of Mexico (see related questions) that would be the Opata language, spoken by 15 speakers in 1993 and almost considered an extinct language.
There isn't a definitive answer to this question as it depends on how "least common" is defined. However, languages like Njerep, Liki, and Dumi are considered some of the least spoken languages in the world with very few speakers.
Animism
Saterland Frisian, one of the Frisian languages (among which include West Frisian, spoken in the province of Friesland in the Netherlands, and the collective dialects of North Frisian, spoken in the Nordfriesland district in Schleswig-Holstein, Germany) is probably the least spoken Germanic language today. Spoken only in the German town of Saterland, it has about 2,000 total speakers, half of whom are native. It is listed as an endangered language.
The least most spoken language is also the largest smallest vocabulary and is largely filled with tiny letters and articles of punctuation. This language, known as crypticclarity, is spoken the least by the vast majority of people who speak it. Most people who speak crypticclarity are at least as old as those who speak English or Spanish or French or the many dialects of Chinese, Korean and other Indochina languages. The least known language amongst most of the world, crypticclarity is only spoken by those who speak it.