The latest versions of DotNetNuke support any XML files as language files - this omits the need of being compliant with ASP.Net resource files, that have a number of redundant header, comment and attributes. If you eliminate all this overhead, some language file (there are 241 for DotNetNuke framework with and all core modules) are reduced in size by up to 95% - and I estimate, about 70 % overall. The size reduction also improves load speed and memory consumption, the more lanugages you have installed, the more this effect will take place.
There are dicussions to integrate this in the future DNN release process, currently I did the conversion manually, you can download the files here, to test the improvements for yourself. If you install the language pack using the command in Host :: Languages menu item, the original resx files will be replaced by smaller XML files - please make sure, that you are applying the appropriate for the core/module versions you are using.
I especially suggest all translaters to use these files, which will act as templates for their own resource files, so they get smaller language files without any extra effort.