Extremely Endangered Languages:
* Ainu: Once spoken in Japan, now only a handful of elderly speakers remain.
* Burushaski: Spoken in the Hunza Valley of Pakistan, with less than 10,000 speakers.
* Svan: Spoken in the mountainous region of Svaneti in Georgia, with fewer than 1,000 speakers.
* Tausug: Spoken in the Philippines and Malaysia, with an estimated 500,000 speakers, but most are bilingual in another language.
Languages with Small Speaker Numbers:
* Guarani: Spoken in Paraguay, with about 800,000 speakers, but many also speak Spanish.
* Quechua: Spoken in South America, with an estimated 8 million speakers, but many are bilingual in Spanish.
* Nahuatl: Spoken in Mexico, with an estimated 1.5 million speakers, but many also speak Spanish.
Artificial Languages:
* Esperanto: A constructed language designed for international communication, with an estimated 2 million speakers worldwide.
* Lojban: A logical language with a focus on clarity and precision, with around 1,000 speakers.
It's important to note that "unknown" is a relative term. Many of these languages are well-documented and studied by linguists, even if they aren't widely spoken.
The best way to find out about a truly obscure language is to research online or consult with a linguist specializing in endangered languages.