I've been struggling alot with getting WPML to actually leave a custom attribute alone, it keeps overwriting it with the value of the original language. So, I have the field "_coloredvariables" in dutch it works as its supposed to, but for other translations I need a adjusted version of the field, I can create that version, but it keeps getting overwritten with the dutch value
Solution: The field was set to Do Not Translate. Changing it to Copy Once resolved the issue.