Q:

Changing icons or graphics based on user geographic location/language?

Inspired by this question on international police icon, I started to wonder 

If there is a reasonably simple way to replace an icon depending on
browser language? 
...and if anyone has come across real uses of this?

I know it seems like an awful lot of work for a webdev, but it would be interesting. Lots of icons are culture-specific, so it would be interesting to try.

A:

Is is possible? Yes. 
Technology-wise, you would do the same thing you'd do for language localisation (see this related SE question for the specificities).

Localization refers to the adaptation of a product, application or
  document content to meet the language, cultural and other requirements
  of a specific target market (a locale). Source

Seems like the definition fits the icon situation perfectly. W3C actually mentions "Symbols, icons and colors" in their list of customisable elements. Just as it happens with content, images are loaded with cultural baggage.
The apple developers site has some guidelines in respect to internationalisation too: 

Create or modify language-specific versions of nib files, text, icons
  and graphics (especially those containing culture-specific images),
  audio, and video for each locale. Source

Now, in regards to the cases, that's a tricky one because it's not easy to hunt down some good examples, but take a look at this:
In Bangladesh, Iran, and Thailand the "thumbs up" gesture (facebook's "Like") is traditionally an obscene gesture, equivalent to the use of the middle finger in the Western world. Apparently nothing happened, but I bet it was something FB's developers and designers had to consider. 
Also, the example from UX.SE cited in the comments has a nice answer (too bad the Q was closed). 

Animal symbols can also be dangerous. For example, owls symbolize
  wisdom in the United States, and an e-learning website may use an icon
  of an owl to symbolize that a user or student is performing well in an
  online course. However, owls symbolize stupidity in some parts of
  Asia, and Asian students may be insulted, not encouraged, by such an
  icon.
Religious symbols can, of course, be particularly sensitive.
  Microsoft’s geopolitical product strategy team once avoided
  embarrassment by preventing the release of the company’s Office XP
  software containing a moon and stars astrology icon that resembled the
  Islamic Hila symbol. When religious symbols cannot be avoided, they
  must be localized, such as when the Red Cross has been adapted as the
  Red Crescent in the Middle East. Source

One thing is sure: This is a job you can't do based on assumptions. Feedback or research is crucial.  
I found this interesting discussion in meta:

Less confusing icons for localized Stack Overflow sites

And some nice related articles:

The Localisation of Visual Content, Images and Icons
Harnessing the Power of Icon Standards
Website localisation: three examples of best practice

A:

Short answer: 
It's best to use good icons in the first place - sometimes providing additional help to aid understanding can still be preferable (descriptive text, tooltips, etc.).
Providing alternatives based on language can be better some of the time, but it will always be more expensive.

Longer answer: 
In any case, it is preferable to use one set of icons that all cultures recognize. This should always be sought over any workaround.
With that being said, as we've seen some cultures have icons for certain things that differ from other culture's icon for that thing. A lot of the time someone from one culture can still understand what the icon in another culture is. However sometimes they can't. What I'm trying to convey with this is that most of the time icons are not an issue across cultures, especially when descriptive text is provided next to it or a once-shown tooltip for harder icons is provided.
Often addressing a website to a particular culture requires changes to content, sometimes requires layout changes, and often other stylistic changes depending on the particular culture as well. This likely requires a separate site or at least a separate page to address this well. 
High-end websites often deal with different languages and cultures of big client bases by offering alternative sites or pages for that language and/or culture. This is usually done by having a link(s) which leaves the decision up to the user. This allows differences of cultures to be addressed more completely.

But if the icons or other small changes are truly the only thing you think you need to change, it is possible to do it based off of the language of the user (though not perfectly). If you choose this, please make sure 

A substantial amount of your users fit into this category, 
The icon actually is better for that culture (research, testing),
That the implementation of switching is done well - purely using JS to detect is not foolproof in any implementation. 

All of this requires more time and therefore more money. Often times it's better just to improve the original icon anyway.

