First you can go to user's profile you're interested in and then check section Languages at the left side.
Read all the listed languages and see if there's your mother language or any other language you speak.
If there's no language listed then the user didn't choose a language for that profile. Then try to make a contact using your language, maybe you'll get a reply.
Also, you can make an advanced profile search where you can search for the profile you're interested in and desired language(s) for communication.