Could you solve the problem? I have the same problem since updating to wordpress 4.9. Deactivating all plugins did not help. Even a reinstall of wordpress 4.9 was not successful.
This is a confirmed WordPress core bug:https://core.trac.wordpress.org/ticket/42574. “MediaElement upgrade causing JS errors when certain languages are in use e.g de_DE-formal”.
The issue applies to any language file in this format: de_DE-formal.
To resolve this, change the WordPress Core to the regular format: de_DE by changing the language in the WordPress admin area (Settings > General). For example, if currently set to “Deutsch (Sie)” instead select “Deutsch”.
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Comments
Could you first try to disable all plugins and check again?
thanks
I will try this and get back to you.
It is probable the same issue like http://forum.muffingroup.com/betheme/discussion/comment/116247#Comment_116247
My wordpress installation is rolled back to version 4.83.
It is a known issue. See here:
https://core.trac.wordpress.org/ticket/42574
http://forum.wpde.org/installation/178372-wp-update-4-9-betheme-options-funktionieren-nicht-mehr-loesungssuche.html
The issue applies to any language file in this format: de_DE-formal.
To resolve this, change the WordPress Core to the regular format: de_DE by changing the language in the WordPress admin area (Settings > General). For example, if currently set to “Deutsch (Sie)” instead select “Deutsch”.
Best regards,
Muffin Group team