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Sources and licences
Last updated: 23 August 2026
Ether Echo's learning content rests on open corpora and dictionaries, built by volunteer communities over decades. Their licences allow this use on condition that they are credited. This page meets that obligation, and gives those projects credit for what they let us build.
Example sentences
Tatoeba, tatoeba.org
Licence CC-BY 2.0 FR. A community database of translated example sentences, designed for language learning.
The Japanese-English sentences from the Tanaka Corpus, included in Tatoeba, are in the public domain.
Lexicon and dictionaries
JMdict and KANJIDIC, Electronic Dictionary Research and Development Group (EDRDG), edrdg.org
Licence CC-BY-SA. A multilingual Japanese dictionary and kanji character database, the de facto reference for over thirty years.
CC-CEDICT, MDBG, mdbg.net
Licence CC-BY-SA 3.0. A community Chinese-English dictionary. It supplies Mandarin meanings and, alone among our sources, their pinyin.
Wiktionary, Wikimedia Foundation, wiktionary.org, extracted by Wiktextract (Tatu Ylonen), kaikki.org
Licences CC-BY-SA 3.0 and GFDL. The source of meanings in English, French, Spanish, German and Russian, and of Russian stress marks, which ordinary writing leaves out.
Morphological analysis
Sudachi, Works Applications, github.com/WorksApplications/Sudachi
Licence Apache 2.0. Splits Japanese sentences into words and supplies their readings.
spaCy, Explosion, spacy.io
Licence MIT. Splits and lemmatises sentences in the six languages other than Japanese, and segments Mandarin, which writes no spaces.
OpenCC, github.com/BYVoid/OpenCC
Licence Apache 2.0. Converts Traditional Chinese to Simplified before analysis.
Spaced repetition algorithm
FSRS (Free Spaced Repetition Scheduler), open-spaced-repetition
Licence MIT. Decides when each review falls, from your past answers.
Voices and audio
The service's voices are produced by third-party neural speech-synthesis services. No human voice recording from open sources is used today; the day that changes, only CC0 or CC-BY contributions will be kept, and credited here.
Spotted a mistake?
If you believe a source is credited wrongly, or that one is missing, write to us at [email protected]. We will fix it.