Different spellings and concepts transform the word into a linguistic and cultural phenomenon.

Iguazu is not a simple word. There is a wide variety of possible spellings. Iguassu (old Portuguese spelling, widely used in English), Iguaçu (Brazil), Iguazu (General Spanish), Iguazú (Argentine Spanish), Yguazu (Paraguayan Spanish), Yguasu (Paraguayan Guarani) Ihguasu (spelling used by Moisés Bertoni) and Yguachu (aché/guayaki version) just to name a few.

Languages such as English, German, Swedish, Norwegian, Dutch, Italian and others use different spellings of "Iguaçu". What defines what spelling to use is the author's cultural or affective bond. Writers with more affinity with Argentina use the “Iguazú” spelling when talking about the Falls. Writers more connected to Brazil use the “Iguaçu” form. Many English—language newspapers spell Iguaçu Falls (BBC, for example) when referring to the Brazilian side of the Falls and Iguazú Falls when they talk about the Argentine side and sometimes they mix the two.
The following spellings have been found in different leaflets, promotional material and websites: Iguassufallen (Swedish), Iguassun putoukset (Finnish), Iguaçu—fossene (Norwegian) Igvasu krioklys (Lithuanian), Iguaçu watervallen (Dutch), Iguassu—Wasserfälle (German) and Iguazú—vizesés (Hungarian). They seem to reinforce that the identification of the author of the text or his or her affinity or not with Argentina or Brazil determines which spelling to use.

The Iguassu spelling, which was official in Brazil until the 1940s’ orthographic reform, is still widely used around the world, especially for the practice of issuing international air tickets based on the International Code of Cities and Airports of IATA (International Air Transport Association) where the symbol for Iguassu as a destination airport is IGU.

All of these spellings lead to heated discussions and require a good deal of diplomacy. An Argentine will never use the spelling “Iguaçu”, and a Brazilian doesn’t feel comfortable using “Iguazu” or any other version except “Iguassu”, which is considered to be an international form and wouldn’t present any difficulty in pronunciation to anyone. There is also the argument that Iguassú and its derivatives have historically had their place in Portuguese in cases such as Fóz do Iguassú (there we have another spelling), Paraguassú and others with or without accent. The historical discussion of spelling is discouraged by those who say that at the time people wrote “Fóz do Iguassú”, Brazil was written with a "Z", the country was formed by "united states" and the capital of Paraná was called Corytiba: so one would go around reading: Carthório Municipal, Corityba, Paraná, United States of Brazil. Today most Brazilians are offended to read “Brazil with Z”, arguing that this is a gringo thing even in English: Caipirinha is the drink of Brasil.

But the whole discussion of Iguassu spelling either with Ç, SS, an S or Z fades away when we notice that considering the great variety of writing systems in the world, there are hundreds of languages ​​that write Iguaçu without C, SS or Z simply because such problems do not exist. It is the case of those who write in Arabic, Hindi, Japanese, Chinese and Russian, using different alphabets, abjads, syllabaries or adapted ideograms. That leads the discussion to a different direction.

In the languages ​​that use the Latin alphabet adapted to their needs, we have the following examples: Cataratas do Iguaçu (Portuguese), Cataratas del Iguazú (Spanish), Cataratas do Iguazú (Galician), Cascades de l'Iguaçú (Catalan), Chutes d'Iguaçu (French) or Cascate dell'Iguazú (Italian). In all those languages, one could find the spelling Iguaçu, Iguazu or Iguassu.

A problem in the case of Spanish is the pronunciation that Spaniards will give to the "z" of Iguazu/Iguazú. It will sound like "Iguaθú" — the pronunciation of "th", as in English, pronounced between the teeth. Since Iguaçu is a Guarani word, such pronunciation would probably make the original speakers of the language crack up laughing. 

Several Slavic languages use the Cyrillic alphabet. Thus, in these languages ​​the question of using “Ç” or “SS” loses importance: Водопады Игуасу (Vadopadi Iguasu, in Russian) and Водоспад Іґуасу (Vadaspad Iguasu, in Ukrainian) are examples of two Slavic languages ​​using the “S” that is equal to "C". Therefore, there is no “Ç”, nor “SS”, nor “Z”.

In the East of the Planet, Chinese, Koreans and Japanese are not out of the discussion when it comes to the word “Iguaçu”, “Iguazu” or “Iguazú”. Yi Gua Su Pú Bú — Iguassu Falls in Chinese (伊 瓜 苏 瀑布), Iguasu Po-Po — Iguassu Falls in Korean (이과수 폭포) and Iguasu no Taki in Japanese (イ グ ア ス の 滝). As it can be seen from the transliteration, the preference, at least in these examples, seems to indicate that it is enough to write Iguassu with an “S” only. To write “Iguasu”, the Chinese language uses ideograms to which it is given approximate sound values for the transcription. In most cases, the resulting sound in Chinese does not have the same meaning as in the original language. Iguasu reads "Yi Gua Su", a word that has no relation to the original Guarani word meaning Big Water. The Chinese tourist guides therefore have to explain to the visitors from that country that 伊 瓜 苏 (Yi Gua Su) means 大水 (Dà shuǐ/Big Water).

There is no mystery about the writing of “Iguassu” in Korean. The word is written in a fully phonetic alphabet with vowel and consonant sounds having a number of letters similar to the number we have in the Latin-based alphabets. The curiosity of the Korean alphabet has to do with the way the letters are arranged — Iguassu in this case does not appear in linear form as in Western languages: 이 (Yi) 과 GuA 수 (Su).
Japanese is a special case. To write Iguassu Falls, three “alphabets” or writing systems are used. Iguasu (イ グ ア ス) is written in a syllabary called Katakana — used to write non-Japanese or foreign words like Iguaçu, Sao Paulo, Gabriela or Uber. Falls (滝/Taki) is written with a letter shared with the Chinese, i.e. an ideogram. Linking Iguassu and Falls, there is the preposition "of" (の) that belongs to the syllabary called "Hiragana", used to write Japanese words either native or imported from Chinese. In short, Iguassu Falls looks like this in Japanese: イ グ ア ス の 滝 (Iguasu no taki) literally, “Iguassu of Falls” — which many people may identify as an expression written backwards.

The Arabic alphabet is not unique to the Arabic language. Other languages ​​of non-Arab peoples such as Persian (Iran), Urdu (Pakistan), and Pushto (Afghanistan), just to name some examples, use the “Arabic” alphabet and in their case, again, the issue of Iguassu with “S” or “Z” is made present (only the spelling with two Ss is out of the question).

In Arabic, Iguazu Falls is spelled Shalalat 1(Shallalat Iguasu) or Shalalat 2 (Shallalat Iguazu). The question of "S" or "Z" is present, once again related to the affinity of the client, the writer, the journalist with either side of the Falls, either Brazil (Iguaçu, Iguassu) or Argentina (Iguazu, Iguazú). The spellings in Persian, ایگواسو آبشار (Abshar Iguasu) and in Urdu اگوازو آبشار (Abshar Iguazu) are good examples of it.
Therefore, the word Iguassu faces the usual dilemma: spelled with "s" or with "z"? Both forms can be found in Arabic; there are websites that talk about Shallalat Iguasu and Shallalat Iguazu. The Iranian can say, in Persian, Abshar 1 (Abshar Iguasu) or Abshar Iguazú Abshar 2 as well as the Urdu who seems to use the same word "Abshar" for Falls.
In any case, Iguassu is a strong name. It is the name of a river, of one of the three largest waterfalls in the world, the name of an entire watershed and it also gives name to different regions of Paraná based on river characteristics such as Lower Iguaçu, Middle Iguaçu and Upper Iguaçu. These denominations also define characteristics of groups of municipalities located in them.
The Upper and Middle Iguassu basins are entirely Brazilian. The Lower Iguassu Basin is shared with Argentina. But it is important to identify a different view for each side. Lower, Middle and Upper Iguassu for Argentina means an area totally different from Brazil. Lower (Bajo) Iguazú for Argentina means below the Falls, Iguazú Superior is the immediate area to the Iguassu Falls, before falling into the Iguassu River Canyon, and Upper (Alto) Iguazú is the area where the Iguazu River becomes international. In other words, the Argentine Alto Iguazú is the Brazilian Lower Iguaçu.

Expressions such as Destination Iguassu, Destination Iguazu or Destination Iguazu are closely related to tourism and are used to spread the tri-national area or the Triple Border * where Argentina, Brazil and Paraguay meet. Visit Iguassu — Institute for Tourism Promotion officially uses Iguassu in its publications. The idea is that Iguassu refers to all the tourist attractions of the region of Triple Border, united in an effort to integrate the peoples and cities of this border area.

Even the term Triple Border and Three Frontiers are the subject of discussion. Traditionally, the region is called by residents as the “Three Frontiers”. Hence the wealth of establishments and entities such as the Rotary Club Three Frontiers, the Three Frontiers Landmark, the Three Frontiers Post Office, the Three Frontiers Allotment; in the last 100 years there has been no Rotary Club Triple Border, a Triple Border Post Office or a Triple Border Landmark.