'Spreken tegen' is not old-fashioned. But you won't see it much. There is a difference between the two. When you say 'ik spreek tegen hem' it means that you're talking to him, but he is not listening (or not hearing you). When you say 'ik spreek met hem' it means that you're actually in a conversation with him.
What you're hearing is that the Dutch S is sometimes palatalized (as in some Scottish dialects of English). This means that the back of the tongue is pulled up closer to the palate as though you're going to say an English
y sound right after the s, but you never actually do. To an English speaker, this can sound a lot like "sh". I hear it big time in the computer's pronunciation of "varkensvlees."
Scots is a distinct language and not a dialect of English. It has its own grammatical structure and rules. Fit wiy div ya nae unnerstan? [For example is the doric dialect of Scots] There are many similar words in Scots and Dutch. We could, if there was a duolingo course in Scots, learn to say "the coo is gan til the kirk".