fix(lang): Update el.json (#8848)

## Description
Updated Greek translation.

## Specific Changes proposed

- Added some missing translations on el.json.
- Updated translations-needed.md.

## Requirements Checklist
- [ ] Feature implemented / Bug fixed
- [ ] If necessary, more likely in a feature request than a bug fix
- [ ] Change has been verified in an actual browser (Chrome, Firefox,
IE)
  - [ ] Unit Tests updated or fixed
  - [ ] Docs/guides updated
- [ ] Example created ([starter template on
JSBin](https://codepen.io/gkatsev/pen/GwZegv?editors=1000#0))
- [ ] Has no DOM changes which impact accessiblilty or trigger warnings
(e.g. Chrome issues tab)
  - [ ] Has no changes to JSDoc which cause `npm run docs:api` to error
- [ ] Reviewed by Two Core Contributors

Co-authored-by: Adam Waldron <acwald@gmail.com>