Changing language settings prompts to restart the browser

[luixxiul]

Closes #4777

Auditors: @bbondy

Test Plan:

1. Change the language setting on about:preferences
2. Click "Yes" on the notification bar
3. Make sure the browser is restarted taking effect the change

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).

Test Plan:

[bbondy]

++