Language overhaul

As a translator of the plugin, I find the overall language used in the plugin quite vague and imprecise. I think that many strings could be made clearer, and some should be made able to translate (at the moment email-strings can't be translated).

The issue names no files, tests, or entry points. Begin by locating the plugin's user-facing and email strings, then inventory which wording is vague and which strings bypass translation. Done means the agreed strings are clearer and all identified email strings can be translated.

Written by the indexing model from the issue text.