Ability to add translations to customize repeating set later

## Description
Having translations for the "add" and "remove" buttons is a requirement for repeating sets, but this should only be a requirement later on, in case people don't have the content/expertise to input that right away

## Steps to reproduce
1. Go to GC Forms
2. Create a form
3. Add a repeating set
4. Customize repeating set
5. Change English content
6. Delete French content which doesn't match anymore
7. See error

## Details
- **Browser**: Chrome
- **Operating system**: Mac
- **Environment**: Production
- **Language**: English and French
- **Viewport**: Desktop
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## Expected behaviour
Ability to leave blank and be prompted to fill in later in the Translations screen

## Screenshots or videos

Start by reproducing the listed steps in GC Forms, focusing on repeating-set customization and the Translations screen. Trace where deleting French content triggers the error and verify that the English and French fields can remain blank initially, with completion prompted later in Translations.

Written by the indexing model from the issue text.