Google Chrome

The Google Chrome browser has an built in option to translate a webpage to another language.

 

However if you want  to translate part of a webpage or selected text, you can install the Google Translate extension from Google which allows you to highlight text and click on the translate icon (or right click) to translate the selected text.

 

Mozilla Firefox

 

For Mozilla Firefox, the Google Translator plugin by Andy Portmen works well to translate highlighted text using the Google Translate service or entire pages via the icon it installs on the menu bar