Japanese

Japanese is essentially 16th-century Chinese, 17th-century Portuguese, 18th-century Dutch, 19th-century French and 20th-century English with an abhorrence of consonant clusters. Matthew Faupel (in John Cowan's Essentialist Explanations)

Yuta Aoki is a man from Tokyo who teaches Japanese online. In a comment on one of his YouTube videos, he gives the following warning about texbooks:

I just remembered this but sometimes, how you phrase your questions makes Japanese people think that you don't speak Japanese very well.

I noticed that Japanese textbooks always (I've checked dozens of textbooks but I haven't found any exception yet) teach you to speak like a 'foreigner' and not like a Japanese person. There are so many expressions that you see in textbooks but you don't really hear in real life.

Learning Japanese (General)

Websites for Learning Japanese Online

Japanese Writing System(s)

Japanese uses a combination of writing systems: kanji (copied from China), hiragana (a syllabary for writing native words), katakana (a syllabary for writing foreign words, loan words, for technical and scientific terms, etc.) and romaji (the Japanese name for the Latin script). Hiragana and katakana are collectively known as “kana”.

Writing System: General Resources

Learning Hiragana and Katakana

Learning Kanji

Dictionaries

Textbooks

Grammar

Other Resources

Other Aspects of Japanese

Proficiency Tests

Japanese-Language Proficiency Test (JLPT)

The Japanese-Language Proficiency Test or JLPT is a standardized (…) test to evaluate and certify Japanese language proficiency for non-native speakers, covering language knowledge, reading ability, and listening ability (Wikipedia: Japanese-Language Proficiency Test). In Japan, the JLPT is administered by the Japan Educational Exchanges and Services (JEES). Overseas, the tests are typically organised by the The Japan Foundation of the Ministry of Foreign Affairs of Japan in co-operation with local educational institutions.

Kanji kentei

Kanji Kentei and Kanken are two unofficial names for the Japan Kanji Aptitude Test.

About the Japanese Language in General

Culture and Everyday Life

Japanese Computing, Font Faces and Typography