The reason it's hard to bolt-on after the fact is that languages conflate the concept of "string" and "user-facing text". If "user-facing text" had a different

The reason it's hard to bolt-on after the fact is that languages conflate the concept of "string" and "user-facing text". If "user-facing text" had a different type or method or whatever, it would be trivial to find all references in your codebase and consolidate them into gettext stuff. But instead, every inline dynamic sql, every dictionary key, every http parsing looks like user-facing text.