How do I display multilingual logos in D7?
For D7, this is very painless.

In i18n, enable 'Variable Translation' module. To do so, be sure to have at least variable 7.x.2.x, else this module is not available. Here is the text from the module page:

Multilingual variables that switch language depending on page language.
Requires: Internationalization (enabled), Locale (enabled), Variable     
(enabled), Variable store (7.x-2.x) (incompatible with version 7.x-1.2),
Variable realm (7.x-2.x) (incompatible with version 7.x-1.2)


After that, go to:

configuration->Multilingual settings->variables (tab)->Theme settings. check the boxes. Then go to your theme and set a logo for each language.

That's it!