query-09677e1f2600de2f839ea8db5766cc61

You could try to extrapolate from:

Use at

https://query.wikidata.org/sparql

PREFIX schema: <http://schema.org/>
SELECT (COUNT(*) as ?count) 
{
    { SELECT ?item { ?uk schema:isPartOf <https://uk.wikipedia.org/> ; schema:about ?item } LIMIT 500000 } 
    ?ru schema:about ?item ; schema:isPartOf <https://ru.wikipedia.org/> .
}

Query found at

https://www.wikidata.org/wiki/Wikidata:Request_a_query/Archive/2019/09

graph TD classDef projected fill:lightgreen; classDef literal fill:orange; classDef iri fill:yellow; v4("?count") v2("?item") v3("?ru") v1("?uk") c4([https://ru.wikipedia.org/]):::iri c2([https://uk.wikipedia.org/]):::iri v1 --"schema:isPartOf"--> c2 v1 --"schema:about"--> v2 v3 --"schema:about"--> v2 v3 --"schema:isPartOf"--> c4 bind1[/"count(*)"/] bind1 --as--o v4