Will I, tall F, be able to shop for clothes?

I�fm 5�f11 and wear a size 12-14 pant/L US. Would I be able to shop for coats, tops, dresses in Japan?

yes

what does F mean?

Female.

I'm going to give you a qualified maybe. It depends on what sort of clothes you are looking for, how short do you like your bottoms and what your proportions are and how much you are looking to spend. Unfortunately, it also depends on which brands in the US you are a 12-14 in. Vanity sizing in the US is very real. I use to have a tall thin friend who lived in Japan and she had a terrible time finding clothes.

I'm a short F and I can sometimes wear Japanese clothes and sometimes can not. I'm older, so I want skirts that are longer than mid-thigh. I can wear an L to XL in Uniqlo, which I find runs larger than most brands in Japan. Some brands only have "one size fits most/Free sizing" sizing. I can sometimes fit in that for skirts, it depends on the length, I can't fit into it for tops. I'm probably between an 6-10 USA, depending on fit and when the clothes were made.

If you like your skirts short, it will make things much easier. If you're not particularly busty, that will help too. Lots of brands have elastic waists for skirts. I think for jeans it will be much harder. I didn't even see any in a size large enough for me to try on, and Uniqlo claimed they carried my size. I'd like to lose some more weight before my next trip because I saw the cutest Disney themed clothing at one store in Shinjuku.

I don't know about Japanese brands, but there are lots of western stores here where you will be able to buy clothes (I'm thinking Zara, H&M, GAP, American Eagle...).
With Japanese brands you might have less luck. I'm 5'1 and 114 lbs and I have a hard time finding pants that fit me at mall stores. Uniqlo has lots of sizes though, it's a pretty safe bet.