[Bug]: Renderer spellcheck API does not work on Windows

[lishid]

Preflight Checklist

• I have read the Contributing Guidelines for this project.
• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for a feature request that matches the one I want to file, without success.

Electron Version

12.0.2

What operating system are you using?

Windows

Operating System Version

Windows 10 1909

What arch are you using?

x64

Last Known Working Electron version

No response

Expected Behavior

renderer.js

let element = document.createElement('textarea');
element.spellcheck = true;
element.value = 'testt';
document.body.appendChild(element);
element.focus();

setInterval(() => {
  console.log(require('electron').webFrame.isWordMisspelled('testt'))
}, 1000);

Expected: Console log repeatedly print "true"

Actual Behavior

Actual: Console log repeatedly prints "false"

Testcase Gist URL

(edit ckerr): https://gist.github.com/ckerr/91b84f22d5beeef1506174b495720dd7

Concerning the API released in #25060

@zcbenz Noticed you were working on spellcheck related tests. It seems that the tests for this API don't run on Windows so it wasn't caught:

electron/spec-main/spellchecker-spec.ts

Line 84 in f08b67f

const shouldRun = process.platform !== 'win32';

This seems to work on Linux for me, but not on Windows.

[lishid]

This comment might be related:
https://github.com/electron/electron/pull/25060/files#r496156887

[ckerr]

Confirmed works on Linux. Tested with Electron 12.0.2 on Ubuntu 20.10.

Electron fiddle test: https://gist.github.com/ckerr/91b84f22d5beeef1506174b495720dd7

[codebytere]

This is because by default the spellchecker only automatically detects language on macOS - see:

electron/docs/api/session.md

Lines 691 to 699 in 45c4dd5

	#### `ses.setSpellCheckerLanguages(languages)`
	* `languages` String[] - An array of language codes to enable the spellchecker for.
	The built in spellchecker does not automatically detect what language a user is typing in. In order for the
	spell checker to correctly check their words you must call this API with an array of language codes. You can
	get the list of supported language codes with the `ses.availableSpellCheckerLanguages` property.
	**Note:** On macOS the OS spellchecker is used and will detect your language automatically. This API is a no-op on macOS.

If you add session.defaultSession.setSpellCheckerLanguages(['en-US']) to your Fiddle before you create the window the test will pass.

[lishid]

I have tried adding session.defaultSession.setSpellCheckerLanguages(['en-US']) in my fiddle right before new BrowserWindow but I can still repro this issue.

An observation is that Electron correctly spellchecks the textarea with English, without having to set the language, but the API still returns false on the identically misspelled word.

[lishid]

@codebytere Can you verify/repro this on Windows?

[lishid]

@ckerr Any chance we can have this re-opened?