Computers were first developed in Britain and the USA, where the language was standardised with an irrational spelling. Dr Johnson's pioneering dictionary accepted most of the standard spellings used by 18th century London printers, and these in turn were a collection of frozen accidents. The new USA missed the opportunity to standardise spelling to their own pronunciation and kept most of Dr Johnson's irrationalities, with just a few small changes like 'color'.
English has more than two hundred inconsistent ways to indicate its various vowel sounds. The same letters can mean different things - thus the æoÆ is short in pot and long in potato. Likewise teas and bears, win and wine, war and wag - not to mention Waugh and Wagner! Only a few recent imports from foreign languagesùcafT, nanve, vis-a-vis, Tclairùare normally given vowel-accents. My version of Microsoft Word will automatically correct to these forms if you enter the unaccented version.
In most European countries, things went differently, with spelling being normalised to the accent of the dominant group and vowel-sounds specified exactly. The rules are consistent for that particular language, though they vary between languages and some languages have special letters that no other language uses. But the USA rapidly came to dominating the new computer industry, and US citizens chose to do things their own way with minimal allowance for foreign customs. This meant that accented vowels were lumped in with 'special characters' as things just a few people use.
For Word, you can enter accented letters using [Symbols] under [Insert]. My keyboard (standard British format) will type acute accents if you press the [AltGr] key and then the letter. Another method is detailed by FAQ68-2616. But that assumes that everything stays on a single type of PC.
Most PCs use ASCII, which is standard for the first 128 characters but variable for the other 128, 'Extended ASCII'. This is because it originated as a code for 7-hole paper tape and it was convenient for US computer developers to work with. (See weblink here for the most common variant.) This also means that an accented vowel entered for one dialect of ASCII will not show correctly for another ASCII dialect used by a different machine. Accented characters may turn into something unprintable. Quotation marks sometimes turn into a
There are also problems with keyboard and character sets. Keyboards mostly have their own codes, which they send to the computer for interpretation. The code may mean something other than what the key physically says. (See weblink here for examples.)
It is also possible to change the keyboard, but this is risky. There was a case reported where a user set her password to a Norwegian word including a Norwegian-only character. Then with Windows running, she switched the default language of her keyboard to French. This made it impossible to enter her password without using Alt. (Details on Tek TipsThread779-937400.)