@koen84,
First download the latest Beta version of qTranslate-X
Edit: download it here
Do not use install via WordPress admin!
First unzip the new file.
Deactivate the existing version of qTranslate in WordPress admin.
Then with FTP delete all files in the existing qtranslate-x folder and after that copy all new files in it.
Activate qTranslate-x again via WprdPress admin.
This has many improvements and new features.
One of these is Highlight Style
When there are many integrated or customized translatable fields, it may become confusing to know which field has multilingual value. The highlighting of translatable fields may come handy then:
Shows a line on the left border of translatable fields.
Now about the class or id:
Settings – Languages – Custom Integration – Custom Fields
In the field id or class place there the name of the class or id.
For example, the class is called – Some-title subtitle
Put it in the class field and save changes.
Then go to the appropriate field and see if it is Highlighted.