wp-admin/includes/class-theme-upgrader.php:55Initializes the upgrade strings.
public function upgrade_strings() { $this->strings['up_to_date'] = __( 'The theme is at the latest version.' ); $this->strings['no_package'] = __( 'Update package not available.' ); /* translators: %s: Package URL. */ $this->strings['downloading_package'] = sprintf( __( 'Downloading update from %s…' ), '<span class="code pre">%s</span>' ); $this->strings['unpack_package'] = __( 'Unpacking the update…' ); $this->strings['remove_old'] = __( 'Removing the old version of the theme…' ); $this->strings['remove_old_failed'] = __( 'Could not remove the old theme.' ); $this->strings['process_failed'] = __( 'Theme update failed.' ); $this->strings['process_success'] = __( 'Theme updated successfully.' ); }Introduced in 2.8.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-admin/includes/class-theme-upgrader.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.