Create a custom function for wordpress

Hi, We have added in our header a closable DIV that displays a message. What we need is : - To detect the language of our visitors (probably by checking the browser lang) - To display a message depending on that language - If the user closes the DIV, the DIV should remain closed for 7 days The expected result is that if a visitor comes to our website and uses a language other than "French", than it displays a message at the top saying our website is also available in English. If the browser of the visitor is in French, no message is displayed. If the user closes the div when it's displayed, it won't appear again as he navigates through the website (until the set period is passed).