Dual language writing

My main language is English, but I’d like to write in Russian too. My keyboard has Russian letters. How can I switch from one language to other?
Thanks for the help!

Which desktop? KDE or Gnome or …?

In KDE you can go to Configure Desktop (from the green Lizard lower left) and then navigate Region … > Keyboard. There you can switch multiple keyboards on and add the keyboard layouts you need. When finished there should be a nationalyty flag in your Panel (lower right) where you can click to switch layout.

When you have enabled multiple keyboards, you can take advantage of them in OpenOffice.

You can also use Tools>Options>Language settings to set a default language for all new documents and to change the default language for a single document.

If you change language, e.g. with Format>Character, you will find that the language is added to the list at the bottom of the page; you can then swap languages for spell-checking purposes within OO as well as swapping the keyboard layout with KDE or Gnome.