Language diversity is valuable
Monolingualism and homogeneity are limiting. We should protect endangered local languages because all cultural identities and languages are valuable and contribute to humanity's linguistic diversity.
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96% of the world's population speaks 4% of the world's languages. Due to a variety of factors (including globalization, colonization, and majority-spoken languages being associated with socioeconomic advancement) many of the world's minority languages are going extinct at a steep decline.
With so much of the world's population speaking only a few languages, linguistic diversity is decreasing as it becomes more economically practical to speak in a few majority languages. Of the world's 6,000-7,000 languages, only a few hundred languages are taught in public domains and less than a hundred languages are present in the digital sphere. Since there are such few languages represented in global affairs, speakers of minority languages are excluded from diplomatic and development possibilities. Endangered languages should be preserved, recorded, and maintained so more people's languages can be represented and celebrated as part of the human tapestry of knowledge, cultures, and ways of communication. In addition, multilingualism is the norm across the world and is associated with a multitude of cognitive benefits. Many studies have found that bilingual children's cognitive abilities (including attention and auditory processing) are better compared to monolingual children. In addition, multilingualism can delay the onset of dementia, and multilingual people showed better decision-making skills. Thus, multilingualism and linguistic diversity are more useful for individuals and should be preserved for more people, as opposed to having monolingualism be deemed as normal and ideal.
Language diversity makes progress more difficult. The reason 96% of the world's population speaks 4% of the world's languages is because it is much easier and more beneficial to communicate in a widely-spoken language. Language diversity also can cause conflict because mistranslations and miscommunications are sure to arise when communicating across languages. Language diversity is not helpful when progress in development can occur much faster through the medium of a few, mutually understood languages.
This argument assumes that diversity is always good.
[P1] Monolingualism limits one's worldview. [P2] Linguistic diversity allows for more freedom, innovation, and more voices to be heard.
Rejecting the premises
[Rejecting P2] Linguistic diversity causes more misunderstandings and inefficiencies than monolingualism.