In case your subtitles look like this:

Non understandable subtitles

you have to follow few steps to solve this problem.

Follow: Start -> Control Panel -> Regional and Language Options

A window will pop-up (see image below)

Advanced tab

Click on the field  Languages for non-Unicode programs and select the subtitles language (for example Greek)

Greek

Press OK. You may need to restart your PC to apply the changes you have done.

After play your movie. The subtitles now works fine.

🙂