Fix logic for setting the locale when using System Default

[ChunkyProgrammer]

Fix logic for setting the locale when using System Default

Pull Request Type

• Bugfix

Related issue

closes #3360

Description

The comparison being done was incorrect and didn't check the country code.

Testing

Test 1 - en-US as system locale

• set system locale to en-US
• Log out and log back in to your computer if necessary (you may need to log out for the change to take effect)
• Run FreeTube
• Set locale to System Default
• (notice that text remains System Default)

Test 2 - en-UK as system locale

• set FreeTube locale to en-US
• set system locale to en-UK
• Log out and log back in to your computer if necessary (you may need to log out for the change to take effect)
• Run FreeTube
• Set locale to System Default
• (notice that text becomes System default)

Desktop

• OS: Linux Mint
• OS Version: 21.3
• FreeTube version: 0.19.1

Additional context

Bug was introduced in #2271

[PikachuEXE]

To avoid logging out to test this
I stub the result by adding return 'en-US' & return 'en-GB' before return app.getSystemLocale()

[absidue]

For the non-electron fallback we can use navigator.languages instead of navigator.language.