See sidebar menu for specific languages
General
BBC Languages: archived but still great
http://www.bbc.co.uk/languages/
Guardian resources
https://www.theguardian.com/education/languageresources
https://www.theguardian.com/travel/languagecourses
Languages of the World
http://www.ethnologue.com/
About the International Language Proficiency Scale
https://www.govtilr.org/Skills/ILRscale1.htm
Omniglot encyclopedia of writing systems and languages
https://www.omniglot.com/
List of Free Online Language Courses
http://www.word2word.com/course.html
for languages that use different alphabets or writing systems, download the appropriate keyboard:
https://keyman.com/
RhinoSpike is an online language learning community tool that lets users around the globe connect and exchange foreign language audio files. Get any foreign language text read aloud for you by a native speaker!
https://rhinospike.com/
Pictorial Vocabulary Guides and Interactive Readings in a variety of languages
https://www.languageguide.org/
PARALLEL TEXTS ROM ENGLISH TO 55 DIFFERENT LANGUAGES
http://www.lonweb.org/
iLoveLanguages is a comprehensive catalog of language-related Internet resource
http://www.ilovelanguages.com/index.php?category=Languages|By+Language
Linkword courses
https://www.unforgettablelanguages.com/
Read children's books in various languages
http://en.childrenslibrary.org/
Lingopolo offers audio resources for learning several languages. It is committed to a free model, and as I write this it is offering lessons in Dutch, French, Japanese, Thai, and Pandunia (a constructed global language like Esperanto).
https://lingopolo.org
Vocabulary trainers
Memrise
https://www.memrise.com/
You Know the Drill
http://www.youknowthedrill.com/
Voca, previously known as Vocatude, is a free vocabulary trainer for Windows and Linux.
http://www.oriente-voca.eu/wordlists.php?lang=eng
VocApp
https://vocapp.com/
anki flashcard software
https://apps.ankiweb.net/index.html
Language Software Reviews
https://www.languagesoftware.net/
Create your own online with Quizlet
The InterActive Terminology for Europe dictionary will give you translation of words for specialized terminology.
Search for words in context to gauge their actual meaning with Linguee. Note for most European languages, and Japanese.