Question: I have a button with image.How can I localize it, in order it to have another image on different language ?

Answer: 
Are you loading the image from a Storyboard or programmatically?

If programmatically, then you can localise the string of the file name and have different images for each localisation.
If your image is not in an xcassets you can localize it in the file inspector. 
If you image is in an xcassets, you can include the language identifier in its name, or as @jdapps said, localize the image name in a strings file.