Follow-up to https://github.com/backdrop/backdrop/pull/2397#discussion_r244554774
Because we have both $active_config and $staging_config, and you've passed in $context above... we could delete the out-of-date strings that are no longer used from the locale table when a string changes. For example if the translation for the registration email changes (or the content of the registration email changes), we don't need to be keeping all the old copies of that translated string in the database, just delete them all with that context key.
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The Mail System and MimeMail modules are now installed. I'll let you know if they solve the problem. Edit: Using Mail System with MimeMail I was able to send plain text emails. There is...
HTML Email treated as plain text
If you haven't already I recommend installing Mail System and MimeMail. The latter will help format emails as HTML and first helps with configuring which module will handle the formatting...
HTML Email treated as plain text
The horrors of cut/paste! Brilliant, thanks.
SQLSTATE[22007]: Invalid datetime format: 1366 Incorrect string value: