spell check hook should use pre-commit/identify instead of length `exclude:` key

[lorenzwalthert]

Just text files that are not R or Python source files, probably that's all we want. https://pre-commit.com/#filtering-files-with-types. Or just recommend other spell checkers like https://github.com/codespell-project/codespell

[mpadge]

Related to this: It would also be useful to have the spell check hook respect the "Language" field in the DESCRIPTION file, where that is given. I've not look at how the hook actually works, so not sure whether this is possible, but as a non-US English speaker, i'm always annoyed at the default reversion to US English spelling.