How to verify if certain russian language text is present in SOAP UI Respone or not

The document content is encoded within the json response.

https://stackoverflow.com/questions/11145681/how-to-convert-a-string-with-unicode-encoding-to-a-string-of-letters

You can use contains assertion with the unicode content

\u044f\u0432\u043b\u044f\u044e\u0442\u0441\u044f

or script assertion to convert from unicode 

import groovy.json.JsonSlurper
def text ='являются'
def response = messageExchange.response.responseContent
def jsonSlurper = new JsonSlurper().parseText(response)
content = jsonSlurper.document.content

assert content.contains("${text}")
log.info content