-There are numerous dictionaries and they're not identical. Plus the work of a dictionary is to collect the meanings they find in use, not to tell people which meaning is proper
-In some countries following The Enlightenment they created official language institutions (like France), they tried codifying languages but they find themselves chasing the native speakers constantly (e.g. the French spelling reform two years ago).
-don't quite get the thing about sounding the same and meaning. two words can be written in the same way but pronounced differently (US to UK version of herb), two words could be written differently but denote to the same meaning 'pants'-'trousers'. The point here is the 'fucking hell' and 'fucken hell' mean exactly the same thing.
-most academic linguists would even doubt the existence of solid grammar for a language let alone rigid spelling rules, the only interest in misspelling is when it is accompanied by some learning disability (knowing the specific lingual conventions but failing to implement them).
-fucken and fucking are different words, the point was that none was more valid than the other to use. you don't err when you write fucken and you're Scottish, like the American doesn't err when he says gas instead of petrol.
-I'm not a native English speaker but I'm guilty of doing this in Hebrew. Correcting spelling 'mistakes' is often a condescending act that allows you to humiliate and disregard the other side without actually listening to what they had to say. Someone is not inherently stupid because he writes 'innit', and spelling correction is a social tool for silencing them or others.