Allow custom dictionary for spellcheck

[PurpleRock]

Use case or problem

There is no spellcheck for Latin language, yet it is available for Chrome on Linux.

Proposed solution

Add Latin as an option for the built-in spellcheck, or let users add their own language dictionaries.

Current workaround (optional)

None.

Related feature requests (optional)

Spellcheck for Language X

This post is to consolidate all the various requests to add support for spellcheck in language other than English. At the moment, we can’t leverage chrome/electron built-in spell check. @Licat made a pull request to electron to add support for interfacing the editor we use and the chrome’s spellchecker. When that goes through, we will have spellcheck in all languages.