I was able to reproduce in a clean sid chroot. Created chroot with debootstrap, chroot to directory, install nodejs, node-y18n
node -e "require('y18n');" internal/modules/cjs/loader.js:583 throw err; ^ Error: Cannot find module 'y18n' at Function.Module._resolveFilename (internal/modules/cjs/loader.js:581:15) at Function.Module._load (internal/modules/cjs/loader.js:507:25) at Module.require (internal/modules/cjs/loader.js:637:17) at require (internal/modules/cjs/helpers.js:22:18) at [eval]:1:1 at Script.runInThisContext (vm.js:96:20) at Object.runInThisContext (vm.js:303:38) at Object.<anonymous> ([eval]-wrapper:6:22) at Module._compile (internal/modules/cjs/loader.js:689:30) at evalScript (internal/bootstrap/node.js:587:27) ls /usr/share/nodejs y18n -- Sent from my Android device with K-9 Mail. Please excuse my brevity.