Setup UI - Fix translation of post-install messages

Setup UI - Fix translation of post-install messages

Here's what happens:

- The "Setup" subsystem does its internal/partial bootstrap; it sets `$tsLocale` and uses `CRM_Core_I18n`. Hooray.
- The "Setup" initializes the database/settings and then does a full bootstrap. The full bootstrap step calls `applyLocale()`, which replaces the active `$tsLocale`... with the *unconfigured default*. Ooops.
- This step runs next - and it updates the DB setting. But we've already trampled `$tsLocale`. Calling `applyLocale()` a second time means we use the preferred `$tsLocale` again. Hooray.