I installed QGIS 3.0.0 on a PC with French as default language. After changing the language of QGIS to English, the 'Vector' menu is empty and there is a French 'Vecteur' menu. Any ideas how to fix this? (I cannot change the system language)
There is already a bug reported for this problem.
In the meantime you can click "Reset to defaults" under Settings > Options > Processing and then restart QGIS. This removes the empty vector/raster menus.
I'm teaching qgis right now and several student have the same problem. The processing plugin deactivate by their self in several laptops. Just go to plugins/manage and install plugins and reactivate it