If both languages are supported equally, then put them both in the body of the email.
If most of your readers are going to be reading it on desktop, you can try putting both languages side-by-side. This can be especially good if one language is read left-to-right (ex: English, Spanish) and the other is read right-to-left (ex: Hebrew, Arabic); readers of both languages can start reading their email in the correct way and see their language first. However, putting the two languages side-by-side requires that you make a lot of assumptions about window size, and is very likely to cause problems if read on a mobile device.
If you are going to support easy reading on mobile devices, you will have to choose an ordering. If the home office is known to primarily use one of those languages, you can put that language first and the other language second. If your readers are predominately reading one language, put that one first. If you're unsure, or if nothing seems quite right, you can alternate which language you put first. You can put a link to jump to each language at the top of the email to reduce the scrolling necessary.
There are very few circumstances where you would not want to put all languages in the email. If you only put one language in the body of the email, and require the reader to click a link to read the contents in the other language, you are sending another message in your email: that readers of the other language are second-class citizens. Further, requiring them to click a link to read the message drastically decreases the chances that they will actually read it.
You can consider adding some tracking to your emails to see which language is read the most. You could also conduct some user research to see if your selected method is effective, such as a simple survey or perhaps lightweight interviews.