@dominikvitt : i think i move whole to

DefaultValue::model()->with('question')->deleteAll('question.qid IS NULL');
DefaultValueL10n::model()->with('defaultvalue')->deleteAll('defaultvalue.dvid IS NULL');

Are there any reason to do find + foreach ?

No, it won't work.
First line would delete all default values where qid is missing, which is correct.
But, second line would leave orphaned DefaultValueL10n rows, because you already deleted default values.

I think best approach is to:

1. update qid = null for DefaultValue where 'question.qid IS NULL'
2. delete DefaultValueL10n where DefaultValue.qid is null
3. delete DefaultValue where DefaultValue.qid is null

In that case foreach loop won't be necessary.

I'm unsure on where to put the function …

Maybe

1. Create QuestionL10n::fixQuestions($isurveyid); (and AnswerL10n etc …)
2. This function get all language from survey, and delete all other QuestionL10n
3. Create SurveyLanguageSetting::fixLanguage($isurveyid)
4. Call all related function in this function

Currently : import any survey, delete : can import it again … even after fixDataIntegrity …

But more : currently : checkintegrity add "checkbox" for each Question. Did we really need to add checkbox ?
Then we need to add checkbox for each QuestionL10n too ?

Maybe best is

1. First step add one checkbox for all fix to do : one checkbox for "Delete X questions"
2. 2nd step delete whole Question using a deleteAll and not a for each …

Fix committed to master branch: http://bugs.limesurvey.org/plugin.php?page=Source/view&id=31367

Fixed in Release 4.4.14+210322