1. If you want to have multilingual site you need use WPML plugin http://wpml.org/ .
2. Yes, the changes will be lost when you update the theme. So to keep them you need make changes in a child theme http://codex.wordpress.org/Child_Themes . Create the same directory hierarchy for the file you’re going to edit.
3. When you use wpml plugin to change currency the color will be the same.
