Sorry, i am not at home this moment.
But i mean, if you start Steam you find in on this side under Options or so a point for this.
But use the link to read how to do this:
https://support.steampowered.com/kb_article.php?ref=2037-QEUH-3335 (https://support.steampowered.com/kb_article.php?ref=2037-QEUH-3335)
one Tip from the Steam side:
Changing the language of the Steam client
The Steam language setting determines which language the Steam client application displays, as well as the language which games are presented in. (Third-party titles may have their own language settings - these settings will generally be independent of the Steam language setting)
1.Log into your Steam account
2.Click the Steam menu in the top menu bar (this is the first option on the left at the top of the window)
3.Go to the Settings option
4.Go to the Interface tab
5.Select the language you wish to use from the drop-down menu
6.Click OK and then select the option to Restart Steam
7.Once Steam restarts, you will be able to use Steam and Valve games in the language which you selected.
8.If you have games installed that support the language you have selected, files for that language may need to be downloaded before you can play.
