Instead, I would use sitecore devices. For each language you can define a site, and each site can have its own device. This will work ready if you have one domain name for each language (www.site.com, www.site.de, www.site.fr, etc.)
If you have one site (one host name) for all languages, you can switch devices using the httpRequestBegin pipeline processor.
This article http://briancaos.wordpress.com/2012/04/12/identifying-mobile-devices-in-sitecore/ describes how to identify mobile devices. It’s easy to rewrite the logic for switching devices depending on the language.
When you define different devices for each language, you simply place the images on a device that matches your language. And you still have the option of a backup device for all those pages where all the visualizations are the same.
Modifying Sitecore's default behavior may work, but using and extending the Sitecore platform is the best way forward.
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