I returned to Mint Tachikawa for the first time in over a year to see if anything has changed and to get a better idea of the store's selection so I could write an updated Card Stores in Japan post. Here are my previous posts: 1, 2, 3.
Prices are standard (60 yen for singles, with inserts generally starting around 300 yen). Cards in the display cases might have been a bit cheaper than usual.
English may be a problem here, depending on who's working the counter. They're younger so they should understand very simple expressions, but my experience shows that the younger generations are frequently afraid to try speaking.
It's located in a mall where each floor is focused on a certain type of store; the fourth floor is the "Hobby and Culture" floor so you'll find a couple other stores that might be worth browsing - an Animate anime/manga-based store, an Americana store, a coin and stamp store, a used book store (which might be temporary), and a couple other things which I forgot already.