The paradox is that it’s hard to have much idea about the potential pitfalls in these older courses before one is already somewhat advanced.
For example, I have an old German Lingaphone course (well, just the book actually) dating from the 1920s or 30s. Now I’m not a native speaker, but I have had some pretty extensive immersion in the German language when I was younger, so I think I have some idea. It’s actually surprising just how much of the 1920s German in this book would still (in my estimation) be perfectly good today - albeit in a rather ‘correct’ and formal register perhaps.
But there are some things in there that would possibly sound a bit antiquated today? For example they have someone asking directions by saying: “Guten Tag! Wollen Sie mir gefälligst sagen, wie ich zum Theater komme.” (I’m quoting from memory so that may not be 100% exact - but it’s something along those lines.)
Well, as I say, I’m not a native speaker. But I feel a little bit unhappy about this use of “gefälligst”. I do suspect (any native speakers, please comment!) that it would sound a rather abrupt way of asking a question nowadays? Maybe even bordering on rudeness?
I mean, if you tell someone: “machen Sie gefälligst Ihren Job!”, well, that would definitely have an aggressive edge to it, I think. So could you really still ask a question in this way!? What I would be inclined to say is something like: “Entschuldigung, können Sie mir sagen, wie ich zum Theater komme?” or something like that.
No doubt there are other things too - that’s one that sticks in my mind.
And yet, if one learned - really and truly learned - all of the content of this old German course, one would be still be streets ahead of someone who had instead learned everything in a modern Teach Yourself book! So, I dunno…
Having checked a dictionary…ehm…well…“gefälligst” may actually still be okay…!? :-()
Either way, there must certainly be some words in this course that will be out of date today…I guess…