There are between 5,000 and 6,000 distinct human languages in the world today, and countless more if dialects are included. All languages have two key elements: abstract symbols and syntax. Abstract symbols stand for something that may or may not be present. Syntax allows users to arrange their symbols in an agreed upon order that expresses meaning. There are many different forms of symbols and syntax. What matters most is that users of any system agree on the meaning of its symbols and syntax.
Language is one form of communication and, by definition, involves thinking. However, not all communication is language. For example, "body language" is a misnomer and may not involve thinking at all. The signals your body gives off are not necessarily abstract and do not necessarily have to follow any form of syntax.
Consider this abstract symbol: "Apple". This English word represents the fruit to us. It conjures up a mental image. However, its appearance gives us no clue about its meaning. This symbol is made up of 'a', two 'p's, 'I' and V. Each of these is meaningless alone; their correct arrangement is what gives the symbol meaning. If the users are able to speak, these also allow for a phonetic element of speech.
Words in other languages function the same way. For instance, the Spanish word 'manzana' is an equivalent abstract symbol for apple.
Humans are the only species able to record their thoughts. Recorded messages, as well as spoken language, allow us to transcend time and space. A woman who records her thoughts in a letter in 1885 can transcend time. Over 100 years later, we have an exact mental image of what she was trying to express in words. Even though she has been dead for decades, we have access to what she was thinking and feeling, assuming that deception was not involved. Today we can transcend the limits that distance imposes every time we use a telephone or send an e-mail. We can immediately know the thoughts of a friend thousands of miles away using these two methods to transmit language.