There are many ways in which the phenomena of language and culture are intimately related. Both phenomena are unique to humans and have therefore been the subject of a great deal of anthropological, sociological, and even memetic study. Language, of course, is determined by culture, though the extent to which this is true is now under debate. The converse is also true to some degree: culture is determined by language - or rather, by the replicators that created both. Language and culture are not fundamentally inseparable. At the most basic level, language is a method of expressing ideas. That is, language is communication; while usually verbal, language can also be visual (via signs and symbols), or semiotics (via hand or body gestures. Culture, on the other hand, is a specific set of ideas, practices, customs and beliefs which make up a functioning society as distinct.
A culture must have at least one language, which it uses as a distinct medium of communication to convey its defining ideas, customs, beliefs, et al., from one member of the culture to another member. Cultures can develop multiple languages, or "borrow" languages from other cultures to use; not all such languages are co-equal in the culture. One of the major defining characteristics of a culture is which language(s) are the primary means of communication in that culture; sociologists and anthropologists draw lines between similar cultures heavily based on the prevalent language usage.
Languages, on the other hand, can be developed (or evolved) apart from its originating culture. Certain languages have scope for cross-cultural adaptations and communication, and may not actually be part of any culture. Additionally, many languages are used by different cultures (that is, the same language can be used in several cultures).
It is also a fact that languages are heavily influenced by culture - as cultures come up with new ideas, they develop.
References: ------------------------------------------------- The Theory and Practice of Self-Formation (Bildung), 1791-1810" in: Journal of the History of Ideas, Vol