It is known that in German the pair <ch> and <ck> must not be separated.
With the 1996 spelling reform, we no longer accept that <ck> can be separated (becoming <k | k>).
Now, knowing that the settings of the various programs should follow these rules (for example the hyphenation patterns for LaTeX), some fonts have ligatures <ch> and <ck>.
In some fonts Adobe puts them in a special dlig lookup (adding that I don't know how to do it, composing with LaTeX and also having other dlig, to activate only this one; but this is not a problem pertaining to this forum).
Now: is it more logical to put them precisely as dlig (with which they are optional) or as a liga, specifying in the metadata that only applies to German? Or in some other way (locl or calt with a contextual substitution rule)?