I was looking for a solution on how to localize my FreeBSD setup. And as you can imagine, it's quiet easy and well documented1.

1. Edit /etc/login.conf and add the following lines:

# Use German keymap
keymap="german.iso"

# Use German (ISO8859-15) console fonts
font8x8="iso15-8x8"
font8x14="iso15-8x14"
font8x16="iso15-8x16"

2. Add a new language group to /etc/login.conf

german|German Users Accounts:\
      :charset=ISO-8859-15:\
      :lang=de_DE.ISO8859-15:\
      :tc=default:

3. Activate your changes:

cap_mkdb /etc/login.conf

4. Run vipw, look for your username and add german after your GID.

username:password:UID:GID:german:0:0:USERNAME:/home/USERNAME:/bin/SHELL

Done!