[BUGFIX] Fix translations in deletion modals

[YKWeyer]

When deleting a contentElement in the page module (TYPO3 11.5.32, GridElements 11.1.0), the confirmation modal doesn't respect the language settings of the user. It is also very unspecific, and doesn't explicitly confirm for deletion (and simply asks "Alert: are you sure?")

German	English

This seems to be caused by the Header.html templates, which tries to read a non-existing (or empty) property and falls back to TYPO3 JS defaults in english:

<a class="btn btn-default t3js-modal-trigger" href="{item.deleteUrl}"
  data-severity="warning"
  data-title="{item.deleteConfirmText}"
  data-content="{item.deleteConfirmText}"
  data-button-close-text="{item.deleteCancelText}"
  title="{item.deleteTitle}">

ℹ️ See the fallback chain in the Modal TypeScript:

const content = $element.data('bs-content') || $element.data('content') || 'Are you sure?';

I couldn't find anywhere, where deleteConfirmText, deleteTitle or deleteCancelText was being set (in both the GridElements extension and in the TYPO3 core), so I assume it was a copy/paste error, or it was an experiment which wasn't implemented until the end.

After fetching the translations from the backend extension, this is how it looks like:

German	English

ℹ️ the title and the content are twice the same in German, but this is due to the two strings label.confirm.delete_record.title and label.confirm.delete_record.content being identical in that locale.

[sypets]

There is already an issue open for this: #45

See also my PR #60