Hi Marek ,
Sitefinity 3.x supports multilingual backend. Sitefinity 4.0 will be release 2010, but there is no certain date yet. The translation process for 4.0 versions will be different from this one for 3.x and we will not use compiled resources. All projects developed or upgraded to 3.7 can be converted to 4.0.
Currently we could send you not compiled localization resources in English that you can translate to any language, then you should return the resources to us. Afterwords we will compile all resources and send the generated dlls to you.
the Telerik team