Sometimes I see
е written instead of
Is this actually a common occurence in written Russian, or an acceptable version of the word?
For example, even Google Translate will not use the diacritical character.
It is perfectly acceptable in modern Russian and you will rarely find any materials with consistently spelt Ё. The letter Ё has a difficult history: it was never really obligatory.
I prefer to always type it explicitly. But according to modern orthography it is completely acceptable to write е instead, except in foreign words, names which can be read incorrectly and other cases where the omission would lead to ambiguity.
The only problem is that people are lazy and omit it just everywhere, even when the omission leaves a reader guessing from context what you exactly mean — which stems from the fact that there are very few cases in the language where Ё is the only way to distinguish two words or word forms. So people just rely on your ability to figure out the meaning from the context. Does not help with the names, though (Соловьев/Соловьёв, Алехин, Хрущёв, Горбачёв) and rare words that speakers started to mispronounce (афера, свёкла, блёклый).
There has been a movement in support of Ё in recent years, and I kind of support the ideas that there is no real reason now to not show the difference (there aren't any keyboards that don't let you).. But, just like with the attempts of making English spelling system less ..er.. outdated (but reflecting the pronunciation of 15-16 century should make you proud :)) — I do not believe it is actually going to happen anytime soon. Just like with English spelling, people just get used to the words they see and use, and then you may spell them with or without proper Ё's — it does not matter.
The letter itself is a relatively recent innovation: Old East Slavic, the direct ancestor of Russian, used the sound [e] instead. There was no need for Ё. But then, curiously, around 13-14 century stressed ['э] became ['o] and [йэ] became [йо] after a soft consonant (but not before another 'soft' consonant!) This was long considered "improper" pronunciation (and not all dialects were affected), and "е" still was used in poetry as far as in 19 century but the more or less modern Russian, as you might guess is based on accent that has Ё.
P.S. Why does Russian have words like "лес" where stressed Е did not become Ё? The reason is, there used to be another e-like sound [ѣ] in Russian which had long merged with the sound of letter "е" by 19 century (and especially by the end of 19 century) in the vast majority of dialects. It was horrible: schoolchildren had to memorise long mnemonic poems made up of words where you should spell the sound with [ѣ] ("Бѣдный блѣдный сѣрый бѣсъ убѣжалъ голодный въ лѣсъ…" as it was spelled back then). So the spelling reform was suggested (had been suggested since the end of the 19 century), and, well, after the revolution of 1917 the Bolsheviks just accepted the project along with many other much more radical things :)
usage of [je] everywhere, i guess was enforced by some church regulations. by resemblance with swears, may be? much of russian swears have [jo]/[je] as their most recognisable part. and perspective representatives are tend to use it almost everywhere, strange to hear sometimes some words said - братья и сестры[sestrɨ], instead of - братья и сёстры. that is a complete guess however.