If you take the time to read WP RSUE you will see that it is common for editors to request translations of material that is being cited that is not in English In this case whoever cited the source should of added a translation just a small quote of what is being cited would have been sufficient Leaving the tag on will be a heads up for the editor who did or to someone who might have access to the source Another option would be to remove the source completely and change the article per the dozens of reliable English sources