Hi Sarah,
You can customize the language of email through administration. (I am assuming you are talking about default emails that Moodle sent like signup confirmation , forgot password etc.)
Go to Site Administration => Language =>Language Customization => choose English (if you are using English) => open language pack for editing
it will take some time then click continue.
Now if you have a mail that you want to change then just put some part of mail in the field "Only strings containing" and select all component in "Show strings of these components"
just write in "local customization" and save changes to language pack.