grammatical question

I believe you're wrong because the noun is in singular

Thanks for a prompt response, evfokas.
As you say, I was wrong, but not because "Wandrer" is singular. Exactly opposite. Because it is plural.
If it is singular, it must be "müden Wandrer" because Wandrer is a male("Wanderin" for female). (In addition, the songs in "Winterreise" are about the one and the same young man.)
I was mistaken because I took "Die" before "müde" as an article, which is actually a "relative pronoun." Without an article, an adjective must be "müde", a strong flection instead of "müden", a weak flection.

Yes I think you're right, it kind of confused me a bit.
I checked it and you're right I expected Wändrer to be the plural

For starters, the noun "Wandrer" is not in singular, but it's not that obvious because the singular and plural forms of "Wandrer" are identical.

To come back to the question: both "müde" and "müden" could be correct. But based on the context "müde" is the proper choice. Let me try to give an approximate translation of that stanza:

You green deads' wreaths
Might well be the signs
THAT invite tired wanderers/travellers
To the chilly inn

The reason why I capitalised "that" is that that's the distinguishing feature. It's a relative pronoun, relating to the wreaths being the inviting signs, if you will. So "müde Wandrer" is accusative plural, hence "müde" is the right form.

Thanks, Floele.
You are absolutely right.
I noticed your point just a little earlier and corrected my former comment.
Anyway, thank you very much.

germany is always easy to learn ,and hope you can insist on learning it

Without an article, an adjective must be "müde", a strong flection instead of "müden", a weak flection.

a strong flection instead of "müden", a weak flection.