Apply existing translation for the data page

[wbazant]

Part of #538.

The /data shows content that used to be spread through /data and /datasets on the live site. See how the translation keys are used on the live site: https://fallingfruit.org/data?i18n_viz=1
https://fallingfruit.org/datasets?i18n_viz=1

Implementation steps:

1. Replace English with translation keys in the component file
   The file to change is src/components/about/DataPage.js.

To test, we expect our helper script to say all of these translation keys which we see on hover under i18n_viz=1 in the live site, are in the component file - run this command:

python3 scripts/translation_manager.py  --component_path src/components/about/DataPage.js --list-in-component

2. Move the keys between locale files

We have a script for this:

python3 scripts/translation_manager.py --component_path src/components/about/DataPage.js --json_folder public/locales/ --yaml_folder ../falling-fruit/config/locales --migrate

3. Compare content

Now you can look at the localhost vs. beta site, and localhost vs. live site, in English and French. The content should be the same!

You can just look at them, or also, comparing text is a good trick - switch to Reader View, copy text from the site, save to a text file, and compare as text files.

4. Submit for review

Don't add any keys yourself in this issue since we will do that later - leave English in the source code, and optionally you can make a new issue that reminds us, but we'll do that later.