Use the _html suffix to mark that we expect the translations to contain links.
Unfortunately, we can't use the _html keys for the plain text emails, since the input options (e.g. username, url) will be html-escaped,
before it is passed to the view. So we need to use non-html-suffix keys for the plaintext views, in most cases. Only when the translation
options (e.g. url) are guaranteed to not contain any escapable characters can the same translation key be shared.
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