define a script type (e.g. Latin characters, perhaps with some rules about non-ASCII characters) or character set (e.g. characters of the German alphabet)
Draft rules:
write valid words in a horizontal or vertical orientation, taking into account script applicable directionalit(y|ies)
start with one valid word touching at least one of the x (e.g. 4) fields in the center
allow
any word in any language using that script, as long as it is indexed as such in Wikidata (or Wiktionary)
Basic idea:
Draft rules: