Anglo-Saxon/Old-English
https://archive.org/details/firststepsinang00sweegoog
Icelandic
https://libgen.li/edition.php?id=136528773
https://archive.org/details/primerofmodernic0000snae
Ancient Greek
https://archive.org/details/athenaze-an-introduction-to-ancient-greek-book-i-pdf
Sanskrit
https://in.yoga/wp-content/uploads/2022/02/A._M._Ruppel_The_Cambridge_Introduction_to_Sanskz-lib.org_.pdf
Lojban
https://youtu.be/KgxOrTvpWJ4
https://en.wikipedia.org/wiki/Lojban
https://lojban.pw/en/books/learn-lojban/
https://la-lojban.github.io/uncll/uncll-1.2.16/xhtml_section_chunks/
linguistics
https://youtu.be/qxOJ4p8e7NQ
https://youtu.be/2_gnZj7gbnQ
https://sharifling.wordpress.com/wp-content/uploads/2018/09/the-study-of-language-george-yule.pdf
https://www.youtube.com/playlist?list=PLUl4u3cNGP63BZGNOqrF2qf_yxOjuG35j
the Trivium
https://archive.org/details/the-trivium-the-liberal-arts-of-logic-grammar-and-rhetoric-sister-miriam-joseph
Analyzing Grammar, An Introduction
https://anekawarnapendidikan.wordpress.com/wp-content/uploads/2014/04/analyzing-grammar-by-paul-r-kroeger.pdf