Dictionaries and network use

Where definitions and translations come from, and what WinDict sends over the network.

The dictionaries

English comes from Open English WordNet, over 150,000 words and phrases, which is built into the executable. Lookups in it don't use the network and take under a millisecond.
Italian comes from Wikizionario, about 67,000 words. It's downloaded once, about 8 MB, when it's chosen under Languages in the settings, and kept in %LOCALAPPDATA%\WinDict\dicts.
The online dictionary is used for pronunciations and for words the built-in ones don't have: Wiktionary, through dictionaryapi.dev, and Wikizionario for Italian.

With both languages chosen, a word is looked up in them in the order they're listed, English first.

A word you look up, to the online dictionary, only when the built-in one doesn't have it or for its pronunciation. Turn off Online dictionary in the settings to never send one.
Text you translate, to Google Translate or MyMemory, only when you ask for a translation.
Once a day, a request to GitHub for the latest version. Turn off Check for updates to stop it.

Answers are kept for a while, so asking again doesn't go over the network a second time.

WinDict uses about 4 MB of memory while idle. The dictionaries are read in place: Windows only loads the few parts a lookup touches.

English definitions: Open English WordNet (CC BY 4.0, derived from Princeton WordNet).
Online English lookups: Wiktionary, through dictionaryapi.dev, falling back to Wiktionary directly.
Italian dictionary and online lookups: Wikizionario, through wiktextract, falling back to Wikizionario's own API (CC BY-SA 4.0).
Translations: Google Translate's public web endpoint, which is unofficial and may change, falling back to MyMemory.