Yes additional spell checkers are possible via plugins. These plugins typically communicate via HTTP API offered by the (usually) paid language checking service. Example of this is LanguageTool which offers free plans. There exists a community plugin for LanguageTool. However using a community plugin for serious writing is somewhat conflicting since you really care about what you are doing if you want to use quality spell checking tools. This essentially means you should use a web browser or MS Word to get best possible support from 3rd party language services.
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