Ok, now I got time to test it and it worked for csv and xlf....
What I have done was to install Joomla, install jdiction, create a article, export jdiction with 'com_content' filter, changed it by hand, imported it and checked if the translation was there...
So csv should work.
On XLF you have to check if the translation tool set the target-tag to "translated".
Here is the example:
<xliff version='1.2' xmlns='urn:oasis:names:tc:xliff:document:1.2'>
<file original='84e82d5cfbf593a3e66580e648a70a09' source-language='en-GB' target-language='de-DE' datatype='htmlbody' product-name='jDiction' product-version='1.4.1'>
<body>
<trans-unit id='1.com_content.article.edit.title'>
<source><![CDATA[123]]></source>
<target state='translated'><![CDATA[ggg]]></target>
</trans-unit>
<trans-unit id='1.com_content.article.edit.introtext'>
<source><![CDATA[<p>123</p>]]></source>
<target state='translated'><![CDATA[<p>hhh</p>]]></target>
</trans-unit>
</body>
</file>
</xliff>
maybe your translation tool don't change this value. Could you check the source file