I installed Polish language pack for Sharepoint, but unfortunately blog sites are not supported. Is there any way to provide translations for particular site collection templates, which are not supported in other than English language?
You can always copy original resx file and rename it to your language specific (in your case something.pl-PL.resx). Then you can translate it manually.
Two main resx files are:
I think 99% of all needed translations are there but you can also check other resx files at those two locations.
You can find some additional info on this topic at:
Keep in mind since you installed Polish language pack you already have localized resx files.
Title of this article is self explanatory: SharePoint 2010 Meeting Workspaces and Blogs are not MUI enabled.
So only 'solution' is in comment posted by @AndersRask (with all disadvantages):
This is not best practice, but sometimes SharePoint forces to do this. We found solution, how to enable additional language for webs based on blog template. It is enough to change couple of values in the content database. It works in many our projects, bugs depended to this solution not found. More detail description here