I think with the values you show in your example you can use a slight variation on what @antonin_d suggested to avoid the issue:
import urllib, urllib2, time
time.sleep(1)
url = "https://api-zbiory.mnk.pl/api/object/" + value.encode()
request = urllib2.Request(url, headers={'Accept-Language':'en'})
return urllib2.urlopen(request).read()
That worked for me with OpenRefine 3.7.7
