This is a demo site. It will be slow at times. And it will have bugs.
Each object in the OpenStreetMap database can have not only one name but one name in every language. The normal, local name is in the "name" tag. Thats the name thats shown on most maps. But you can also add tags like "name:de" for a German name or "name:ru" for a Russian name. See the list of language codes.
This multilingual map gives you, the user, the choice which language tags you want to see. This is done by rendering background-tiles without any labels and overlaying them with a "labels" layer which is rendered on-demand in whatever language (or languages) you choose. Of course not all labels are translated into all languages so there is always the fallback to the normal "name" tag. As more and more labels are translated this will get better over time.
The map style is based on the German Style (developed for the map at openstreetmap.de) which is based on the main style used on osm.org. I have split the one style into two and not changed much else. Although highway shields and house numbers are not translated, they are also rendered in the overlay to reduce overlapping of labels. (There are a few labels that are in the background layer such as tram stops, thats just because it is a bit fiddly to get all of these straight and I haven't done the work yet.)
The demo site runs on the same machine as the tile server for openstreetmap.de using the same database. It can't take away too many resources from the production tile server, so it is sometimes slow. Background tiles up to and including zoom level 10 are pre-rendered. The rendering database is updated every few minutes, but existing background tiles are not expired. Label tiles are cached in memory for some time, there is no expiry policy yet.
The tile server software used is based on the Mapquest Render Stack with modifications from me.
This was developed within the context of the Multilingual maps wikipedia project.
Contact: Jochen Topf