Since iCleanLanguage does only one thing, it doesn't have a whole lot in terms of fancy, but at least it does what it is supposed to well. First you can choose which languages you want to be deleted from your Mac (English is a default and will be saved no matter what). You can also put applications and files in the Exclude list, and these will be untouched by iCleanLanguage no matter what.
You can also choose how thoroughly you want iCleanLanguage to be run. It can do anything from clearing one folder or application of unwanted languages to clearing your entire computer.
Then there is the removal of the languages itself. If you are leery, you can do a dry run that will not erase any language files, but will simply locate them.
I ran a dry run and a run on Everything (except Applications and Utilities) and they both worked fine. However, iCleanLanguage did slow down my other programs quite a bit, so I suggest running it when you are not going to need your computer for an hour or more.