1. Open http://docs.unity3d.com/Manual/index.html
2. Select Russian language (http://docs.unity3d.com/ru/current/Manual/UnityManualRestructured.html)
3. Select Japanese

Result: Ends up at url http://docs.unity3d.com/ru/ja/Manual/UnityManualRestructured.html, which gives a 404 Not Found page. Only happens for Japanese, not e.g. Spanish

- In User Manual, change language to e.g. Spanish and then to Japanese. Result is you end in http://docs.unity3d.com/es/ja/ which is 404 Not Found