User blog:Kyodaisuu/Interlanguage link

I wonder how interlanguage link works. In the page of Up-arrow notation, language link to Knuth's pijlomhoognotatie, dutch page of up-arrow notation, is shown. In the same way, I tried to link to 矢印表記, Japanese page of up-arrow notation, by 矢印表記, but it didn't work. Here it is written that "Interlanguage links are not created by default on multilingual wikis, because the “same” projects in different languages can have very different domain names and database names and must be enabled manually", but it is not written how we can setup multilingual wiki. Does someone know how?