Manually delete unused languages from macOS Yes, I know there are apps like Monolingual, Mackeeper, iCleanLanguage etc. that can do that for me but I would feel more comfortable doing it myself if it is not too much of a hassle. How can I do that?

Also if there are other files I can manually delete to free up space - please let me know.
The language files for each application are stored in

APPL.app/Contents/Resources/LANG.lproj


Removing them for non-standard applications is easy (especially from Terminal), for standard applications you need to disable SIP first.

The space gained by removing them may be small though, they use about 1.3 GB in my Applications folder with about 350 applications installed. Also you need to redo this with every upgrade. You probably gain more by removing a few unused non-standard applications.