The reason of this characters problem is probably because of your locale settings.
Indeed, If you try to run the command locale from the command line and from a cron job, you may get different results such as:

LANG=en_US.UTF-8
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_PAPER="en_US.UTF-8"
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT="en_US.UTF-8"
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=

LANG=
LC_CTYPE="POSIX"
LC_NUMERIC="POSIX"
LC_TIME="POSIX"
LC_COLLATE="POSIX"
LC_MONETARY="POSIX"
LC_MESSAGES="POSIX"
LC_PAPER="POSIX"
LC_NAME="POSIX"
LC_ADDRESS="POSIX"
LC_TELEPHONE="POSIX"
LC_MEASUREMENT="POSIX"
LC_IDENTIFICATION="POSIX"
LC_ALL=

As you can see, the cron job is not using UTF-8. That must be the problem!

So the question now is how to change the locale settings for the cron job?
Some people say that you need to add the following environment variables to the crontab entry:

SHELL=/bin/bash
LANG=en_US.UTF-8
LANGUAGE=en
LC_CTYPE=en_US.UTF-8

But this actually didn’t work for me.

What you can do instead is create (if not already present) the file /etc/environment and add the following line:

LANG=en_US.UTF-8

The cron process will read this file when it starts, so you need to restart it in order to apply the change:

service cron restart

Hope this will fix your characters problem.