This is a constant struggling point of mine. Most of my settings take place in fictional worlds often inspired by various parts of human history.
For instance, one of my stories is located in an Ancient Egypt inspired world. (EDIT : My setting is only based on Ancient Egypt and the clothing is not accurate to what it really was like back then. My characters wear anachronistic clothes.)
In these worlds I am creating, people, well, obviously, wear clothes. Although description is far from being one of my writing strengths (I avoid this weakness by making it part of my style that I don't describe much), I almost always picture very clearly in my head the characters and the way they dress up. In fact, as I am not so bad at drawing, I even use to draw them and their outfits.
The thing is, well, I can't — and it would be stupid to try — ever avoid describing things. Sometimes, it really is important to explain the reader some details he cannot invent by himself. While just writing descriptions is a little problem in itself for me, the worst part of it is describing outfits.
Words like t-shirt, for instance seem really out of place in fictional and not futuristic worlds, like the Egyptian one I mentioned above. But when what my character wears is basically a t-shirt, how do I describe it?
Also I have to mention that I write in French and we use the English words t-shirt, shorts, sneakers or pullover as is, which seems even wronger when used in fictional worlds. But not only English words cause me problems: scarf, for example, for which we have a French word, seems out of place when describing a long piece of cloth the character is wearing around his neck, but not to keep him warm (when in the Egyptian setting it is even worse). Even trousers is weird in some settings.
A trick I often use for lack of a better way is to blandly refer to clothes with very generic words like haut (French for top):
He was wearing a white top and a long piece of cloth around his neck.
See the above example. It is really generic and doesn't tell me much about, for instance, the length of the sleeves of the said top. Or basically anything about it. Moreover, if I have to describe several characters' outfits at once, it quickly becomes boring and makes it harder for the reader to see the characters in their mind.
[Character1] was wearing a dark blue top and a long bottom1. [Character2], however, had a long piece of cloth around his neck and a red top with long sleeves. His bottom1 was short and stopped just above his knees.
1 Not sure this word can be used in this context in English. Sorry if not.
Where I could have just said:
[Character1] was wearing a dark blue t-shirt and and a pair of trousers. [Character2], however, had a scarf around his neck, a red pullover and was wearing shorts.
(Dumb example with dumb clothing)
Well, this is it. I'm sure there is no best way but I'd like to know what techniques you employ to describe clothes similar to ours in fictional words where the modern words we use seem out of place.
I'm writing in French but I believe the problem is quite the same, although even worse in my case.