Please help us help you and fill where relevant:
LimeSurvey Community Edition   Version 6.15.22 
Own server (local server)
Survey theme/template: theme design based on vanilla
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In the previous version 5.6.xx , when I run a form with several languages I can change the language in the top of the form
see image. 
Now, I can't, it is gray
Can I miss something in the form/global setting or it's not an option in version 6.15.xx?
Thanks
Michael