Karabiner (KeyRemap4MacBook) config file

private.xml

<?xml version="1.0"?>
<root>
  <item>
    <name>Krin-San's remapping</name>
    <item>
      <name>Use F19 as non-cycle layout switching</name>
      <appendix>Install Seil plugin to override CapsLock (https://pqrs.org/osx/karabiner/seil.html.en)</appendix>
      <identifier>change_inputsources</identifier>
      <autogen>__KeyToKey__ KeyCode::F19, ModifierFlag::NONE,     KeyCode::VK_CHANGE_INPUTSOURCE_ENGLISH</autogen>
      <autogen>__KeyToKey__ KeyCode::F19, ModifierFlag::OPTION_L, KeyCode::VK_CHANGE_INPUTSOURCE_RUSSIAN</autogen>
    </item>
  </item>
</root>

You should install Karabiner, grant Accessability access to it, write the config above into private.xml. Then install Seil, change a CapsLock key to F19 and follow the instructions below the check box to turn off default CapsLock behaviour.