Even in the US, the sizes for clothing can vary a lot, depending on where you shop.
Trousers, as in slacks or jeans, usually are labelled with waist and inseam, but occasionally I've seen jeans marked only as S, M, L, XL etc. I find it impossible to fit into any of those sizes.
Even when marked with waist and inseam, changes in styles make it uncertain what you'll get, since the length from waist to crotch (the starting point for the inseam length) have varied quite a bit recently. (There seams to have been a resurgence of the "stuffed codpiece" concept, only slightly disguised, among recent teen/tween buyers.)
Shirts (in non-stretchy cloth) should give neck size and arm length (I look for something around 17 x 33 which gives me a somewhat loose neck; but I never wear neckties). These sizes are useful, but sometimes misleading, since the "yoke width" may vary by quite a lot, and an unusually wide yoke demands a shorter sleeve for approximately similar fit.
Even "dressy" shirts are also very frequently found only with S, M, L, XL, XXL or 2XL, and XXXL or 3XL. Rarely the SML sized things will have a fine print "38 to 96 chest" to explain how they determine the size. Here, one might assume the "chest range" is in inches, but that appears not to be invariably the case.
Anything "stretchy" will usually be marked only by size groups, S, M, L, etc..
The biggest problem with finding clothing is the "marketing mantra" that anything that reaches 8% of sales is the only thing stocked. Since idiot children are the most prominent "faddists," and buy far more than the magic 8% of clothing, at many places you can only buy clothing "styled" for obese 9 y.o. tastes. (That may account for some of the apparently large numbers of 20 - 40 year old buyers who appparently do choose to dress like a child?)
While a few years ago you could beat the faddist buyers at the mass market shops by going to a more exclusive (higher priced) seller, even the more sophisticated shops have begun "following trends" to the extent that serviceable and comfortable clothing can only be found by dedicated search expeditions demanding perseverence and a well-stocked debit card (although I still prefer to write a check just for the pleasure of annoying the unhelpful "help").