It's an attempt at command injection.
IFS is basically a space in this situation, and
&& executes multiple commands. So you have:
/language/Swedish && echo 610cker > qt && tar /string.js
Which tries to execute three commands:
/language/Swedish <-- where the injection takes place
echo 610cker > qt <-- write 610cker to file qt
tar /string.js <-- compress file string.js (but the command is invalid)
The commands do not really make sense and are not used to exploit your system, but likely used to test if it is vulnerable.
If you google
610cker you will find some reports about an exploit on a D-Link router (although the payload looks slightly different) and other systems (see eg here, using the same payload).
As with all log entries of this type, it is almost certainly a scanner. If your system is not vulnerable and there are no other signs of intrusion, I wouldn't worry about it.