Hi Tinkerpuss...
Open up your gmail account and you'll see a little cog in the top right corner of the page, this is for gmail settings.
Click on the little downward pointing arrow next to it and it will drop down a menu.
Click 'Settings' and a new interface will load and at the top of this you will find language settings and a 'gmail display language' drop down menu.
Select the language you want and then scroll to the bottom of the page and click 'Save Changes'
Hope it helps.