On the other side we have the individuals inheriting such codebases and being told to add multilingualism when a bunch of other soft dependencies and assumption

On the other side we have the individuals inheriting such codebases and being told to add multilingualism when a bunch of other soft dependencies and assumptions exist which make this entire thing a disaster to implement. It is fairly small and trivial to add so please, if you foresee an event where systems have to support multiple languages and odds are you won't work on it yourself, prepare the damn codebase for it.