Show menu items in all lower case, as that is what they will be saved as

[jidanni]

In openstreetmap/id-tagging-schema#1426 the user is about to manually type in items from the menu.

But as the menu does not represent the reality (all lower case), the user might try to enter a Capitalized name. Yes, it might not matter, but why make the user worry about if they have the case right?

The items should be just like they will be when saved: shown to the user in all lower case.

Yes, even if it looks not as good.

[k-yle]

This is an intentional feature, the labels are localised. In English sometimes the only difference is capitalization. For other languages, the translated labels might be very different to the raw OSM values.