Add i18n to index start and end date format

[Rahmon]

Description of the Change

This PR adds i18n to index start and end date format.

Alternate Designs

Benefits

Possible Drawbacks

Verification Process

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

#2489

Changelog Entry

[felipeelia]

Sorry, @Rahmon, I guess I should've been clearer in my comment before. What I meant is that we should have this value stored in the index_meta as something that could be translated at a later point in the process. So, let's say we only store a timestamp or a datetime format (YYYY-MM-DD HH:mm:ss). So, just when outputting it here we'd translate it.
As is now, if an Italian user starts the sync, a Brazilian user won't have a way to receive the info in a properly translated string. Thoughts?

[Rahmon]

@felipeelia I've updated to store the date in ISO-8601 format and made the date translatable in JavaScript. Could you review it again?