There are some language writing systems which have special marks that are added to some letters in certain words to denote something special about that word. For example in Spanish an accent symbol is added to the main vowel of a syllable to denote that that syllable has the stress.
Particularly in Spanish, the accent mark does not change the vowel in question in any way. For example an accented A letter (á) is still just a regular and plain A letter. There's nothing special about it. The accent is, in fact, not related to the letter in question at all, but to the word in which it appears. It tells something about the word rather than the letter. The accent doesn't make the letter in any way a different letter, and the Spanish alphabet naturally doesn't list accented vowels separately.
What really grinds my gears is when people assume that this same feature happens in all languages with all special marks added to letters of the alphabet, and consequently they think that, like in Spanish, the mark doesn't actually change the letter in any way, and the marked and the non-marked letters are completely equivalent and interchangeable.
This is true in Spanish, where the accent mark is not related to the letter it appears on. However, it's certainly not true in Finnish.
The Finnish alphabet has two umlaut vowels: Ä (a-umlaut) and Ö (o-umlaut).
Now let me make this completely and absolutely clear: The letter Ä is not the same as the letter A. They are completely different letters and have nothing to do with each other. They are listed as separate letters in the Finnish alphabet (on almost opposite ends of the alphabet, no less), they are pronounced differently, they act as completely different and independent letters in words, and they are most definitely not interchangeable. Just because they happen to look similar (with the only difference being the two dots on top) doesn't mean that they are the same or even related!
The same applies equally to Ö and O. They are completely different and separate vowels, have nothing in common and are not in any way interchangeable.
Removing the two dots from the letter changes the letter to a different one. Changing an Ä in a Finnish word to an A is no different than changing eg. an E to an U: The meaning changes completely.
There are even many words which differ from each other only in those vowels, and they are completely different and unrelated words. For example the Finnish word säde (ray) has absolutely nothing to do with the finnish word sade (rain). They are two completely different and unrelated words. (They probably don't even share any common etymology.) They are most definitely not interchangeable.
Thus it really grinds my gears when people from other countries freely and carelessly just leave the two dots out. It doesn't work like that! You are changing the letters to completely different, unrelated letters. Usually the result is gibberish, and in a few cases you are actually changing the word to a completely different, unrelated word.
The ice hockey player is named Selänne, not "Selanne". The latter doesn't mean anything. It's not a Finnish surname. Likewise, the Formula-1 racer is Räikkönen, not "Raikkonen". The latter is not a Finnish surname and doesn't mean anything. It's gibberish.
What really grinds my gears is when the Finnish words and names are mistyped even when there wouldn't be any technical reason for not writing them correctly. For example, I don't think there exists any technical reason why Selänne's shirt couldn't have the Ä instead of the wrong letter A. Nevertheless, they put the A. Why?
Is it because they don't want to confuse the American viewers? Exactly how would they be confused? Perhaps some viewers might start suspecting that, maybe, the name is not pronounced like "selanne" but somehow differently? And why would that be a bad thing? Because, after all, it is pronounced differently. The Finnish vowel Ä is pronounced differently from the vowel A.
There are some languages with umlaut vowels where it's an accepted custom that the umlaut vowels can be changed to non-umlauted versions by appending the letter E. For example Ä becomes AE and Ö becomes OE.
Let me also make this completely and absolutely clear: This is not so in Finnish. This is not an accepted custom in the Finnish language, it doesn't work and, moreover, if you do this the resulting word will become even worse gibberish than by only removing the dots. It actually becomes very hard to read.
For example, the word "vaeaetaeinen" is gibberish. It doesn't mean anything, and it's quite hard to read and decipher. (The correct surname is, of course, "Väätäinen", which is a normal Finnish name.)
Yes, I know that some Finnish sport committees make this precise change to Finnish names in international contexts. However, this is not an accepted custom, nor even a working one. The result is gibberish.
The most obnoxious example I have seen was in a ski jumping competition which was held in and televised from Germany: All the German names were written correctly, with all the umlauts and special German characters. However, all the Finnish names were raped to "aeaeaeoeoeaeaeoe" gibberish. Clearly there was no technical reason why this raping was done, as all the German names were shown correctly.
Please stop raping foreign languages. Finnish is a beautiful language, and it really grinds my gears seeing it raped like this. Just stop it.