Hiding language names in "Language switcher" block and displaying only country flags
OK, in the meantime I found the perfect solution which I earlier just simply overlooked: there's a really simple configuration option in Language icons module's settings in http://&lt;yoursite&gt;/admin/settings/language/icons (D7: http://&lt;yoursite&gt;/admin/config/regional/language/icons) .

You have to set "Icon placement" option from "Before link" or "After link" to "Replace link", which results in displaying only the country flags.

Here are some screenshots (on the admin site I'm currently using RootCandy Dark):

BEFORE:



AFTER (on the admin site):



AFTER (on the main site's right sidebar [design is strongly under development :P]):