Make all templates localized with translation.json

Ref: #1272
Let users customize the strings in Email and SMS templates by editing translation

Start by tracing how Email and SMS templates load and render their strings, then inspect the translation.json handling and the scope described in #1272. Inventory the templates that need coverage; the work is done when users can customize all relevant Email and SMS strings through translation.json.

Written by the indexing model from the issue text.