I have a book somewhere around here that is in (Brazilian) portuguese and it has umlauts in it. Actual, honest-to-god, heavy-metal style umlauts.
The Umlaut – or Trema in portuguese – is the pair of dots that appears above some vowels, mainly in germanic languages. They change the sound of the vowel, usually allowing it to be sounded instead of blending into another vowel like a diphthong.
As far as I can tell from the book, the Brazilians mainly seemed to use it in situations where you have a qu sound but you really want to pronounce the u. So there would be a difference between the que in “Freqüência” and “queda”: in the first it would sound like the que in the english word “frequency’, but in the second it’s just more like a standard que. It was dropped from european portuguese orthography in 1945 but the Brazilians kept using it, officially till the most recent acordo ortográfico. Now, I’ll let you speculate about whether Brazil’s decision to hang onto the Umlaut in 1945 might have been related to an influx of new arrivals from an entbusiastic umlaut-using european country at around that time, but I couldn’t possibly say.
Anyway, it’s officially baninated, but you can occasionally see examples in the wild. Here, for example.
Luso 