I haven't looked at how it's done in your app, but I'd encourage you to make that switch visible for everyone, because you could have e.g. a Spanish person working from the US.

Critical elements are everything that the customer will see: Mainly invoices, but also client area (if you have this), payment page, proposals, emails, etc.

And thanks for the offer, but I've already found something that suits me (Pancake), so I'm not really looking to switch at this time. Just reminding you of something that Anglo-centric devs often forget!