Most editors do support spellchecking and quite often each project has a list of spelling exceptions, a local dictionary that is stored inside the project.

At this moment this is not standardised but .editorconfig would be the best place to document the filename of this exception dictionary (exception word list).

Also another option related to this would be to specify the spelling languages used by the project as some are using US English, some are using UK English or even other languages. Use of same ISO codes as HTML would be recommended for portability (en, en-us, en-gb, ...)

spelling_language=en-gb
spelling_wordlist=custom.dic

Most spellcheckers do support "dic" files which are nothing else than list of words, each on a newline.