electron: SetLocale through app.commandLine.appendSwitch not working

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• 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 an issue that matches the one I want to file, without success.

Issue Details

• Electron Version:
  • 5.0.0
• Operating System:
  • Windows 10 (1709)
• Last Known Working Electron version:
  • 4.1.5

Expected Behavior

I expected calling app.commandLine.appendSwitch('lang', 'el') and then later at app ready event that calling app.getLocale() would return “el”

Actual Behavior

Calling app.getLocale() returns “en-US” that is the system locale currently set on local machine.

To Reproduce

Run this code in main process:

var electron = require('electron');
var app = electron.app;
app.commandLine.appendSwitch('lang', 'el');

app.on('ready', function () {
  console.log(app.getLocale());
});

Additional Information

Problem exists even if there is a browserWindow created before the console.log Chromium window also uses the wrong locale.