This week I came across an interesting problem. The WordPress site I was working on was using Formidable Forms + WPML + the Formidable Forms WPML add-on.
To translate forms using this combination of plugins, you go to Formidable, click on the form you want to edit, and then click on Settings and Translate Form.
When I first entered a translation, it worked fine and appeared on the front end.
When I later went back to edit the translation, the edit updated and saved successfully on the backend. I was even able to see the updated string in WPML -> String Translation.
However, the edit would not show on the front end. After plenty of troubleshooting and an eventual ticket with Formidable Forms support, this was diagnosed as a bug with Formidable Forms.
There is not currently an ETA on a fix for this, but in the mean time, the work-around is to re-create the form field that needs the edited translation. Once you have re-created the form field, make sure you have your translation PERFECT and enter it again. Now it will show on the front end.
I hope this saves someone from the troubleshooting headache I endured.