Language is, indeed, fascinating in itself whether it applies to the written or spoken word. Take, for example, "knee" or "knock" - today we pronounce those words with the "k" being silent. However, the "k" USED to be pronounced.
Language is fluid. Meanings can and do change - I will post a couple of examples from my language myths book when I can. If I remember correctly, there are words we use today that is different from their original usage and slight variations on spelling.
But another example of this fluidity is in the coining of new terms - e.g. "mini-mind" led to "mini-van" and so on. To make something sound more scandalous, it's common for the media to tag on "gate" at the end which is a legacy of Nixon's "Watergate". An example of this is Janet Jackson's "Nipplegate" non-event.
Fluidity in language can relate to changes in pronounciation, assigned meanings and emerging words. You could certainly argue the fact that regional dialects of language in the United Kingdom demonstrates the fluidity of language even there is a standardised form of it widely used. Examples - Ulster-Scots and Cockney are languages that exist in spite of the general population speaking standard English yet knowing very little about those two.
Any discussion on language fluidity opens up a can of worms somewhere along the line.