YouCubed from Stanford University aims to provide research-based resources that are accessible and practical

Math, Science & Music brings together these three subjects with interactive and visual resources designed to engage students of all ages, as well as a number of teacher toolkits

Middle School Chemistry is a nice site with lessons and activities for grades 6-8. It also a Spanish version

The Physics Classroom has branched out, and now includes a section on Concept Builders for chemistry

Ted-Ed has a lesson for each element in the periodic table. Each lesson has a video at its core.

FUN WITH ARABIC is as an online program that teaches the basics of the Arabic language.
http://www.funwitharabic.com/

Free Beginner's 'Introduction to Mandarin' Tutorial
http://www.chinese-outpost.com/language/

news in bilingual texts
https://chinadialogue.net/en/

audio and video lessons
https://www.chineseclass101.com

Chinese Character Flashcards (Traditional Version)
http://animation.archchinese.com/arch_flashcard.html

Learn Japanese For Free
https://japanese-online.com/

Japanese Core 100 Word List
https://www.japanesepod101.com/japanese-word-lists/?coreX=100

Kanji Koohii! is a website and community dedicated to help you complete the kanji learning method called Remembering the Kanji.
https://kanji.koohii.com/learnmore

companion to TV programme: videos, exercises, vocab lists, etc
http://www.tokureo.maori.nz/index.cfm/1,188,0,43,html/Episodes

100 Māori words every New Zealander should know
https://nzhistory.govt.nz/culture/maori-language-week/100-maori-words

Read Matthew, Mark, Luke, and John in Greek over the course of a year, one day at a time
http://www.mythfolklore.net/gospel/

Ancient Greek textbooks
https://www.textkit.com/greek_grammar.php

Reading Homer
http://community.middlebury.edu/~harris/HomericProlegomena.pdf

Calvin and Hobbes en Español
https://www.facebook.com/calvinandhobbesenespanol

Newspapers

Spanish news items especially for use in classrooms
https://www.tweentribune.com/category/spanish/

http://elpais.com/

Interactive Activities for French Teachers and Students
http://www.zut.org.uk/index.html

RFI
https://savoirs.rfi.fr/en/apprendre-enseigner

french grammar
https://www.laits.utexas.edu/tex/gr/index.html

Learn French by watching French videos in an online video player designed for language learners.
https://french.yabla.com/