Hi All,
The problem is caused by "chromium-args" in package.json.
Per NW.js version:
NW.js version < 0.64.0, "chromium-args": "--enable-multilingual-spellchecker --enable-features=WinUseBrowserSpellChecker"
NW.js version >= 0.64.0, "chromium-args": "--enable-spell-checking"
To switch on and set the languages use following code in your JavaScript:
chrome.settingsPrivate.setPref('browser.enable_spellchecking', true) // false to disable
chrome.settingsPrivate.setPref('spellcheck.dictionaries', ["en-US", "de-DE"], "null", ()=>{}) // set the languages
Dictionaries are automatically downloaded.
Have a nice day, Okido