Only use an icon if it leads to a better understanding of your label. Avoid using icons without text. Otherwise you end up with cryptic icons and although it's clear to you and the client what they stand for, visitors to your site will be confused. If your label is not clear, try to rewrite it before using an icon to clarify its meaning. Don't try to re-invent the wheel.
Icons can better visualize clickable zones, together with lots of other design techniques.
Try using these first. Language choice is often visualized with an icon of the national flag. This can be frustrating for some language groups. In a country like Belgium, you never see the Belgian flag, but always the French and the Dutch. Creating a good icon requires money, time, and a lot of inspiration.