How to change default language of front end site

hello, any clue how to change the default language for the front end site?

I use this steps and it worked well, tks.

Second Problem: "Spanish language for OSProperty"
==> ONLY WHEN THE DEFAULT LANGUAGE OF JOOMLA IS SET TO SPANISH AND WORKS
1. If the language files for Spanish are translated to your business, you can go via FTP to the "Joomla root / Language"
2. Then go to the Folder "es-ES" and copy the file "es-ES.com_osproperty.ini" to your Desktop
3. rename "es-ES.com_osproperty.ini" to "en-GB.com_osproperty.ini"
4. via FTP go the folder "root/language/en-GB" and backup the original en-GB.com_osproperty.ini
5. put the new en-GB.com_osproperty.ini (the rename created) to the folder

6. Do the same procedure in the folder root/administrator/language with these files:
--> es-ES.com_osproperty.ini
--> es-ES.com_osproperty.sys.ini