Adding my five cents, I should note the following:

• binding a country flag to a language is OK, as long as it is not an ambiguous binding. Language is one of the distinctive features, which allows to tell apart nations, thus using national country flag is fine. The case of multi-national countries can also be easily handled: for example, Ukraine is a multi-national country, with over 20 nationalities residing on its territory; over 75-80% of all the citizens consider themselves Ukrainians, and the only state language is also Ukrainian; thus, if I see somewhere Ukrainian flag in the “Languages” or whatever section, I will know for sure that if I click that flag, I’ll read the site in Ukrainian. However, one should avoid ambiguity: e.g., in the case of Switzerland (both with multiple nations AND official languages), flag is not an identifier of language. But: I suppose, there is always “the country of language origin”, the flag of which can be used to denote language, and thus author’s claim that “it’s wrong” to bind flag to languages is inconsistent (please comment if you know examples disapproving my point).
• author argues that flag image “eats” more bandwidth than a text representation of the language. Well, true, but not completely: a small GIF/PNG flag image might take less than 200 bytes, and it will be cached on the first request – all the subsequent page loads will not ask for the flag image. Moreover, 300 bytes is nothing compared to the minimal page size of 40-60 KBytes.
• author says: ‘In Web documents, an image can (and should) be accompanied with an alternative textual presentation of the same information, the so-called ALT attribute of an IMG element. For languages, this is easy, but then you can in fact ask what you need the image for in the first place.’ Following this lead, web-pages should be cleared from any images. The flag image ‘in the first place’ is needed for faster comprehension of the fact of another language version availability.
• I am not the “knight of flag-only usage”, language name given in that language is a good solution. But nothing stops from using both flag and language name (in that language) to achieve both fast recognition and disambiguation.
• ISO language codes are evidently less readable and recognizable than flags, and they can be no less ambiguous. For example, country ISO code for Ukraine (and also TLD – Top Level Domain) is UA, but 2-letter ISO code is ‘uk’ (do not confuse with Great Britain English).
• Finally, not using language symbols at all (in the way proposed by the author of that article) is not possible. How would then someone inform the visitor that other language versions are available, if the visitor came to a page not through the site’s navigation, but via the search engine?

That seems to be it. Next time I hope to have a look at the i18n (internationalization) capabilities of Drupal CMS. Stay tuned!