If there's no language id, it's true that it won't be selected automatically anyway. But, it might overlap with another language. I'll take a look and see if zero is a good option to avoid that. If not, is there a totally invalid language id you've been using for Breton? If Breton is based on French, something like MAKELANGID(LANG_FRENCH, 0x20) might be a good idea. MAKELANGID's documentation even states:
For a user-defined sublanguage, usSubLanguage is a value in the range 0x20 to 0x3F. All other values are reserved for system use.