Yomitan от Darius Jahandarie

Yomitan helps you to decipher texts in 20+ languages which would be otherwise too difficult tackle.

Yomitan provides powerful features not available in other browser-based dictionaries:
💬 Interactive popup window for displaying dictionary definitions.
🔍 Search page for easily looking up words.
🌎 Support for more than 20 languages ranging from Japanese to Spanish to Arabic.
🔊 Play native pronunciation audio from multiple sources with the ability to add your own custom audio sources.
📝 Automatic flashcard creation for the Anki flashcard program via the AnkiConnect plugin.
📚 Add multiple dictionaries from recommended and custom sources. Slang, kanji, and pronunciation dictionaries. There are thousands of available dictionaries online
☁️ Works fully offline. No internet connection needed.
💲 Completely free and open-source.
🛡️ Privacy-conscious: we transmit only the minimum amount required of data outside of the extension by default (i.e., we only transmit the single word you are looking up if and only if you click the audio playback button on it). All data transmission is configurable. More information is available in our privacy policy.

More info: Yomitan Wiki