single tap right shift to simulate command + space to select previous input method, however holding right shift still remain the modifier key.

Karabiner_change_input.xml

<?xml version="1.0"?>
<root>
    <inputsourcedef>
        <name>MY_CHINESE</name>
        <inputsourceid_prefix>
            com.apple.inputmethod.SCIM.ITABC
        </inputsourceid_prefix>
    </inputsourcedef>
    <inputsourcedef>
        <name>MY_ENGLISH</name>
        <inputsourceid_prefix>
            com.apple.keylayout.US
        </inputsourceid_prefix>
    </inputsourcedef>

    <vkchangeinputsourcedef>
        <name>KeyCode::VK_CHANGE_INPUTSOURCE_MY_CHINESE</name>
        <inputsourceid_equal>
            com.apple.inputmethod.SCIM.ITABC
        </inputsourceid_equal>
    </vkchangeinputsourcedef>
    <vkchangeinputsourcedef>
        <name>KeyCode::VK_CHANGE_INPUTSOURCE_MY_ENGLISH</name>
        <inputsourceid_equal>
            com.apple.keylayout.US
        </inputsourceid_equal>
    </vkchangeinputsourcedef>

    <item>
        <name>Change Input from English to Chinese by Tapping SHIFT_R</name>
        <identifier>private.inputEngToChs</identifier>
        <inputsource_only>MY_ENGLISH</inputsource_only>
        <autogen>
          __KeyOverlaidModifier__
          KeyCode::SHIFT_R, ModifierFlag::SHIFT_R | ModifierFlag::NONE,
          KeyCode::SHIFT_R,
          KeyCode::SPACE, ModifierFlag::COMMAND_L | ModifierFlag::NONE
        </autogen>
    </item>

    <item>
        <name>Change Input from Chinese to English by Tapping SHIFT_R</name>
        <identifier>private.inputChsToEng</identifier>
        <inputsource_only>MY_CHINESE</inputsource_only>
        <autogen>
          __KeyOverlaidModifier__
          KeyCode::SHIFT_R, ModifierFlag::SHIFT_R | ModifierFlag::NONE,
          KeyCode::SHIFT_R,
          KeyCode::SPACE, ModifierFlag::COMMAND_L | ModifierFlag::NONE
        </autogen>
    </item>
</root>