It would be nice if the composer window featured a spellchecker. Sonnet is one nice candidate, but there shouldn't be a hard dependency on KF5. I'm thinking about an optional plugin. Getting this into the CI and into the autobuilds for Windows is going to be a *lot* of fun :(.
Thank you for the bug report. As this report hasn't seen any changes in 5 years or more, we ask if you can please confirm that the issue still persists. If this bug is no longer persisting or relevant please change the status to resolved.