This endangered language atlas, published by UNESCO, has some amazingly good interactive language summaries! To research, select a search parameter (e.g. location, number of speakers/endangeredness) and several pinpoints will appear, with summaries of each language and sources relating to the language. To browse generally, there’s a scrolling sidebar in alphabetical order! This is an amazing resource. Thank you United Nations! For whatever reason, neither Silbo or the whistled language of Turkey show up – but this is still an excellent resource for research into other endangered languages.