Lpksetup /uand uninstall any possible duplicate language you find there, restart Windows and wait a few minutes. Worked for me after scouring the Internet for hours.
This also provided some users with relief but did not work for me.
Right-click the Indexed folder → Properties → Advanced → Check Allow files in this folder to have indexed in addition to file properties.
Click Apply and Exit.
If it is already checked, uncheck it → apply → recheck it → apply and wait a few minutes for the folder to be reindexed.
Reference machine was a Lenovo T400 with a clean install of Windows 10.