[twic]

Don't push back. That is, don't try to stop them doing this. It is absolutely within the product owner's purview to change and enlarge requirements at any time.

But make it clear to them when they do this that there is a cost. "We estimated building the profile page based on doing it in one language; we can certainly internationalise it now, but it will take quite a bit longer". It's then up to them to decide whether the cost is worth the benefit.

As long as you are working as well and efficiently as you can on the work you have been given, you can feel satisfied with yourself.

Unless of course you're being judged for schedule slips caused by your product owner, in which case you're screwed, and you should quit and find a job somewhere less awful.