Translation interface adds context/location filters and new StringContextInterface

A new StringContextInterface has been added to support filtering translatable strings by context and location in the translation interface (/admin/config/regional/translate).

User interface changes

The translate interface UI now includes "Context" and "Location" filter dropdowns.

API changes

A new optional interface:

namespace Drupal\locale;

interface StringContextInterface {
  public function getContexts(): array;
  public function getDistinctLocations(): array;
}

StringDatabaseStorage now implements this interface.

Example

$locale_storage = \Drupal::service('locale.storage');

// Get available contexts and locations.
if ($locale_storage instanceof \Drupal\locale\StringContextInterface) {
  $contexts = $locale_storage->getContexts();
  $locations = $locale_storage->getDistinctLocations();
}

Backward compatibility

No BC break. This is a new optional interface.