Speakers of the English language use the words "thank you" to express gratitude. Some variations of this phrase include "thanks," "thank you very much" and "I appreciate it."
You can expand the words "thank you" to be more personal and to express a deeper form of gratitude. Be specific and go into detail: thank someone for his support or generosity or contributions and let them know how much you appreciated it or how his help greatly affected the outcome.
Omniglot.com provides a list of ways to say "thank you" in different languages. To thank someone in French, use the word "merci." To thank someone in Spanish, use the word "gracias."