Hi Lewis. I'm Greg, an installation specialist and 9 year Windows MVP here to help you.
I understand you already tried installing another language and reinstalling the pack.
Try uninstalling the Language packs, restart PC, create a new Local Admin account following http://www.howtogeek.com/226540/how-to-create-a..., sign into it, then try adding the Language pack to see if it works better.
If so move your files over and when ready delete the old Account in Settings > Accounts > Family & Other People.
You can then change the new account to a MS account if desired.
https://www.tenforums.com/tutorials/5375-switch...
If not then sign back into your old account and delete the new one.
I hope this helps. Feel free to ask back any questions and keep me posted. If you'll wait to rate whether my post helped you, I will keep working with you until it's resolved.
________________________________________________________
Standard Disclaimer: There are links to non-Microsoft websites. The pages appear to be providing accurate, safe information. Watch out for ads on the sites that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the sites before you decide to download and install it.