For 5.4, 2014.09 and 5.3.3:
As 5.3 is a stable version, only the bc changes are introduced in 5.3, see below for further changes introduced in 5.4.
- Introduce new $useAlwaysAvailable argument for ContentService methods allowing language filtering, false by default
- Update Search service to pass $fieldFilters 'languages' and 'useAlwaysAvailable' to ContentService->load(), set it to true if not set.
For 5.4 and 2014.09
- Change default $matchAlwaysAvailable value of LanguageCode Criterion to true
- Change default value of $useAlwaysAvailable to true
Important reminder for 5.3 and 5.4: LanguageCode criterion still must be specified in the search query if one wants to filter by language. $fieldFilters is only present to filter translations on each and every returned Content objects.