Spelling dictionaries exist for some languages, and help with typing correctly. They are very large for some languages (English), smaller for others (Hebrew), and don't exist at all for most others.
Lexical Wikidata will include words and grammatical information in many languages. It would be good to have a way to export directly this from Lexical Wikidata to a spelling dictionary file that would be usable in Firefox, LibreOffice, LanguageTool, Microsoft Office, macOS, etc.
This is similar to T186420: Lexical Data user scenario: Make it possible to export lexical data as Apertium dictionaries. A spelling dictionary is probably simpler than a machine translation dictionary because it doesn't need to export grammatical properties, but it does need to export all the forms of words that can be written in texts, so it will be a requirement to generate complete conjugated paradigms of all the words.