The main snack shop in Ameyoko is called Niki no Kashi; it is huge, very affordable, and extremely popular with tourists (http://www.nikinokashi.co.jp/). No sampling, no Japanese knowledge required. A lot of the tastes repeat themselves, the crackers are just in different shapes; or you can usually visually guess the flavour (soy, sesame, plum, seafood).

You can also find a good selection in the supermarket Seijo Ishii, or even just head to the nearest Family Mart or 7-11 to buy small packs to try, so you have a good idea of what to get when you go to Ameyoko.

Or you can go sample in the fancy supermarket depachikas, take a photo of what you like (flavour name), then try to match that elsewhere. For the most part you need not know how to read Japanese, as the visual cues can get you 95% of the way.