getLanguage -> getPreferredLocales

[TurtleP]

Summary of the Pull Request

Changes love.system.getLanguage() to love.system.getPreferredLocales() to be compatible with LÖVE 12.0's API.

Validation Steps

Created the following main.lua and ran on 3DS and Switch

function love.draw()
    local locales = table.concat(love.system.getPreferredLocales(), ", ")
    love.graphics.print(locales)
end

function love.gamepadpressed(joy, button)
    if button == "start" then
        love.event.quit()
    end
end

Checklist

• Closes #NA
• Successfully builds

Screenshots

Additional Details

I'll probably have another pair of eyes look at the actual ISO-639 codes. Aside from that, it works. This will also break other people's games if they used love.system.getLanguage(). Not sure of the impact, but hopefully it is minimal.