bat already digs .proto (which is the schema language of https://protobuf.dev).

.textproto is a file format for representation of protobuf data in text format, see https://protobuf.dev/reference/protobuf/textformat-spec/.

The goal of this issue would be to add syntax highlighting support for that format.

I dunno if e.g. https://github.com/VcamX/protobuf-syntax-highlighting could be helpful for someone interested to implement this.