While doing deployment on servers, I was encountered with the error “Update-SPSolution : Cannot uninstall the LanguagePack 0 because it is not deployed.” In order to solve this issue do the following steps:
Find the exact cause: Check the farm solutions by navigating Central Administration >System Settings > Manage farm solutions and you must see error in front of your solution name. There may be multiple reasons why this error came. Error description might help you to find the exact solution. In my case it was saying access denied to few files. I removed the “Read only” attribute from those files.
Resolution: Uninstall/Remove the solution using “Uninstall-SPSolution -Identity <wsp solution file name>”.
Next Add solution again using: “Add-SPSolution -Identity <wsp solution file name>”.
Now intall it again using :”Install-SPSolution -Identity <wsp solution file name> -GACDeployment -Force”.
In case, you get any error doing above steps then last option is go to services.msc stop and restart the SharePoint Timer service and the SharePoint Administration service.
Then run the power shell command again. this time the WSP got updated.
Happy SharePointing :)!!!