Make locale() read only?

The locale system was written so that locale() serves not only for loading existing translations but also for adding a string to be translated if it is not already registered.

The purpose of this was to ensure that code-based strings were available for translation via the UI even if a .pot file did not exist or had not been imported.

However, the fact that anything passed through t() will end up in the locales_source table has led to perennial misuse of t() throughout contrib.

We've tried to address this problem through better documentation, e.g #336115: Additional documentation for t(), but that's unlikely to be tremendously effective.

Another drawback of the current approach is that strings aren't available for translation until they have been displayed somewhere on the site. This means sites admins must return periodically to search for new strings that may have appeared, rather than being able to deal with them all at once.

The alternative would be to make locale() read only. That is, it would only load existing translations. Adding a string for translation would require explicitly calling a method for adding a string.

In practice, sites wanting to translate their interface would need to install the potx module. And we'd need to extend potx to directly extract and add missing translations to locales_source.