Actual:
mw.logObject(mw.uri.encode('Metallica/Kill+\'+Em+All', 'WIKI')) =Metallica%2FKill%2B%27%2BEm%2BAll
Expected - behavior should be exactly as urlencode:
{{urlencode:Metallica/Kill+'+Em+All|WIKI}} =Metallica/Kill%2B%27%2BEm%2BAll
since mw.uri.encode doesn't work as expected one should bypass it and use frame:preprocess('{{urlencode:'..s..'|WIKI}}')