Here is what you have to do:
Just fix the locales with this process:
First run locale
to list what locales currently defined for the current user account:
$ locale
LANG=C
LANGUAGE=
LC_CTYPE=fi_FI.UTF-8
LC_NUMERIC="C"
LC_TIME="C"
LC_COLLATE=fi_FI.UTF-8
LC_MONETARY="C"
LC_MESSAGES=fi_FI.UTF-8
LC_PAPER="C"
LC_NAME="C"
LC_ADDRESS="C"
LC_TELEPHONE="C"
LC_MEASUREMENT="C"
LC_IDENTIFICATION="C"
LC_ALL=
Then generate the missing locale and reconfigure locales to take notice:
$ sudo locale-gen "en_US.UTF-8"
Generating locales...
en_US.UTF-8... done
Generation complete.
$ sudo dpkg-reconfigure locales
Generating locales...
en_US.UTF-8... up-to-date
Generation complete.
Now, that will fix both your locales, but also it will default your language to english to fix the problem.
For more view this: How do I fix my locale issue?