Partial i18n for Upload component

Flow
1

In the JavaScript source code of the Upload component, I read [the following comment]
(https://github.com/vaadin/vaadin-upload/blob/639accc7f7d0d849ed7cf433c67078bf13f55248/src/vaadin-upload.js#L316-L317)

      /**
	   ...
       * For changing the default localization, change the entire
       * _i18n_ object or just the property you want to modify.
       ...
	  */

Now I’d like to change “just the property I want to modify” from the server side. But if I use something like

UploadI18N i18n = new UploadI18N();
// set several porperties of i18n, but not all
upload.setI18n(i18n)

I’ll get an error within the frontend like “TypeError: this.i18n.uploading is null”.

Using upload.getI18n() doesn’t work, as it returns null initially.

Is there something I’ve missed?