i18n: use locale for all numeric formatting in the report

The titles for the new diagnostics (although I predict any ICU plural we use with an explicit "1") are not rendered properly with non-standard numeric representations.

This is because the ICU decleration for the "1" case is explicitly an `en` "1".
```javascript
displayValue: `{nodeCount, plural,
=0 {No elements found}
=1 {1 element found} // this uses the literal "1"
other {# elements found} // this uses the number, like the character "١"
}`,
```