andynador a Russian translation does exist: https://extiverse.com/?filter%5Bq%5D=russian
As to the warning, it means that you have to be aware that upgrading to stable (0.1.0) might require you to get your hands dirty with changing some tables and/or tracing bugs. In the end many forums already run Flarum and with success. If you aren't afraid of an occassional bump in the road during an upgrade, you should be fine running Flarum in production. This is especially so if you have a local/dev install which you test drive changes on.