Change locale string alias logic

Currently, an alias defined in `locale-en-US` is only effective there.

Change it so that it's effective for all locales, *except* if said locale has its own alias or string definition

Locate the code that resolves aliases defined in locale-en-US and trace how other locales inherit or override those values. Verify the precedence between a shared alias, a locale-specific alias, and a locale-specific string definition; done means the shared alias applies across locales unless either local definition exists.

Written by the indexing model from the issue text.