The following issues are known bugs. However those are not fixable inside EXT:news as it needs changes in the the framework below!
The strategy of extbase is currently quite simple. Imagine the default language "English" and a 2nd language "German". If the german news records should be rendered, the following (pseudo query) is used:
SELECT * FROM tx_news_domain_model_news WHERE sys_language IN (german,-1) // all records which are either in german only or in "all languages" OR sys_language = 0 AND not yet translated
see the class Typo3DbQueryParser->addSysLanguageStatement().
After that, an overlay is done to correct the records by calling PageRepository::getRecordOverlay, see the class Typo3DbBackend->doLanguageAndWorkspaceOverlay()
If you are using a language mode like strict, this is the time when the record is removed from the resultset because there might be now translation available.
Out of this reasons, the following things don't work out of the box: * Sorting records in a translation by a translated field * Using strict mode and a pagination