The locale of the browser can play a large part in the rendering of the product and the way that it functions.
It’s a simple test idea that could highlight potential multi-language issues, especially if your site actively supports multiple languages.
The process of changing your browser locale is different in each browser but a quick web search should give you the information you need.
For example, in Firefox on MAC:
Firefox > Preferences > Content > Languages
This will give you a dialogue where you can change the language locale of the browser.
Your browser locale (language) settings will steer your browser to look for “locale specific” content in the sites it loads.
So if your site is intended to be used in English and French markets and will change the language of the landing page(s) depending on the browser locale detected, then try removing all locales and see what happens.
How about adding en-us instead of en-gb – does it still render in English?
You can quickly start to build up a number of tests and further areas to explore.
Try using a Browser Extension to make changing locale easier.
The locale of the browser and the language of the Operating System are two different things.
Quick Locale switching extension – https://addons.mozilla.org/en-US/firefox/addon/quick-locale-switcher/
Changing Windows language – http://msdn.microsoft.com/en-us/library/ms144258.aspx
Changing MAC Language – http://support.apple.com/kb/HT2490#l6
If you want to talk Testing – catch me later this year at EuroSTAR conference.