As far as I understand, delta uses bat for its syntax highlighting, etc… And bat supports having a config file (bat --config-file /path/to/file or by setting BAT_CONFIG_PATH), I'm interested in the second case BAT_CONFIG_PATH.

In this file you can have some file mapping like this for example:

--map-syntax '.gitconfig.local:Git Config'
--map-syntax '.zsh*:Bourne Again Shell (bash)'
--map-syntax '.vimrc.local:VimL'
--map-syntax 'vimrc:VimL'

But it seems like this is not being picked up by the bat version used by delta