[UPDATE]
1 - Solving the HTML parsing problem.
The first thing I had to do was to add the suffix “_html” to the key I created in en.default.json. To quote the docs:
“You can add the suffix _html to the description level of your translation key to prevent translated content from being escaped.”
This is a link to that section of the docs that talks about this feature.
So the updated key became:
"privacy_accept_html" : "Having read the {{ pages['privacy-policy'].title }}><\/a>, I accept its terms."
This indeed created an tag… but the _html suffix didn’t seem to parse the two {{ pages[‘’] }} bits.
2 - Retreive title and url of the policy page from the page object and put them in the snippet
This is the section about “interpolation” that solved my problem
To quote the docs:
“Translation strings can be interpolated, meaning you can include variables in your strings to be dynamically populated when the string is referenced in Liquid.”
And also:
“With interpolation, it’s possible to pass multiple arguments, separated by a comma (,).”
The solution was to put a placeholder, in the string, that would be populated in the contact form template.
I rewrote the key to be like this:
"privacy_accept_html" : "Having read the {{ privacy_title }}><\/a>, I accept its terms."
creating two placeholders {{ privacy_url }} and {{ privacy_title }} to be populated during page rendering.
Then on the contact form template I changed the snippet in this way:
This solved the problem.
3 - A last hicup
I suffered a last hicup when I used the theme content editor to add a translation to the string.
I discovered that while in the theme code editor the string had to be escaped… in the theme content editor you don’t have to escape special characters.
Took me a couple of hours to get to destination, but it was an interesting journey 
