Refactor msgids in PO files

[thekaveman]

Historically, we've treated the msgid in PO files as more of an identifier for the text of the msgstr. This is not the default behavior of language files in Django, however: https://docs.djangoproject.com/en/4.2/topics/i18n/translation/

More typically, the msgid is the text copy in the default language of the site, and the msgstr is used to override the default in different languages.

We continue looking for ways to simplify management of the app copy, we should refactor our PO files to follow this standard model.

Needs #1581 to be completed first.

Todo

• In the English PO file, replace all msgid with the corresponding text in the msgstr
• In the app, replace all references to a prior msgid with the corresponding English text
• Delete the Spanish PO file This isn't necessary
• Run bin/makemessages.sh to regenerate the Spanish PO with new English msgid and blank msgstr