The blog module presents problems with localization for obvious reasons.
I don't have a lot of experience with localization and only just started dealing with it in the past month for a client who wants multi-languages on her site. We're using the Delisoft Localizator since the Apollo localization modules did not support search functions, at least not that I could see. Apollo would work nicely as long as you don't your text content included in the dnn search index. When using the Localizator with text modules, it's pretty easy to enter two modules, one for each of the two languages we are using, then use the Localizator module show/hide function with the language selection to filter content based on language selection.
With the blog module, we tentatively plan to use child blogs, one child for each language and make the appropriate entries in each child blog for each language. I have no experience using child blogs but assume that the site visitor can select a child blog to view and only view entries for that child blog, and, in this case, filter the languages in doing so. There may be a better way of localizing the blog module, and I'm curious what others have done to handle this. This use of child blogs is one idea that may or may not work well, hopefully the former. We may also attempt to see if we can place the child blogs on separate pages and then use the Localizator to show/hide the pages based on language selection, but the blog module itself may still allow or show both languages anyway; I don't know enough about child blogs and how they work to know exactly what will happen and what options we will actually have to implement this. Again, I'd love to hear how others have approached localizing the blog module, too, or if they have gone to third party modules to do this.
Also, I would not recommend customizing the blog module itself. You then end up with a module that can't be upgraded without custom programming it all over again at each upgrade. I leave the core code as is and work around its quirks and limitations to avoid problems with upgrades, especially since DNN is fairly active in development, enhancements, and frequent upgrades.
Rick