Scope and involvement in the style guide workgroup
I'm going to hold off announcing this as part of the style guide effort until we've figured out what our individual scopes are. The style guide suggestions all pertain to content at the English localisation. This means that language concerns brought up by the style guide do not involve localisation unless it is to advise that certain types of content be placed in another localisation. I think your policy idea is mainly about how to utilise localisation? Let's try to clear that up.
Two other things. The first is that I'm not sure what sort of collaboration you are looking for, here. The style guide has a process and formats, that you are welcome to adopt, so that it is clear to everyone that they are welcome to and know how to contribute. The second is that if you are intending on designing a policy, rather than a guideline, it probably doesn't fall under the scope of the style guide workgroup. The topic of localisation may not at all. I think I'm seeing this as more of a localisation-wide policy on how to get, and interact with individual localisations. It is something that English-localised language guidelines would frequently reference. How does that sound to you?