•  You can hide english language if this is enought for you (Admin->Settings->languages->Edit wanted)
• You can rename english language to something else and translate (Admin->Settings->languages->Edit wanted)

You can remove it, but must be sure if you  translate everything on website to your other language before this.

If yes, then:
1. Just for security backup everything

2. Open phpMyAdmin and  run SQL:

UPDATE `language` SET is_locked=0 WHERE 1

3.  Now you can remove language from admin interface Admin->Settings->languages->Remove wanted language