Yes, but not the default way because it's not supported. Since Evernote uses MySpell, you can download the language package from Debian.
Download Debian package: http://ftp.us.debian.org/debian/pool/main/o/openoffice.org-dictionaries/myspell-af_3.3.0-4_all.deb
Note: I've selected Afrikaans language by default.
Install 7Zip using the following link: http://www.7-zip.org/
Right click the .deb file then 7ZIP> Extract file and select a location. Inside the extracted folder you will have an archive called data. Use 7Zip and browse it, then follow the path:
data.tar\.\usr\share\hunspell. You will have two files:
Now, copy these files to the correct directories:
C:\Program Files (x86)\Evernote\Evernote\Dict on a 64bit version
C:\Program Files\Evernote\Evernote\Dict on the x86 (32bit) version.
After the files are copied, go to Evernote and enable Spell Checker for the installed language. Go to Menu > Tools > Options > Language. Locate the Spelling group box. Choose the language you installed and click OK, and you now have Afrikaans language installed.