In Japan, Mothers' day is indeed celebrated. It is called "haha no hi" (母の日).
Me, being an idiot, planned on buying flowers for my host mom until I realized the day before that I had utterly run out of money (I'm not even exaggerating, we went to a party and when no one was looking stuffed snacks into my bag). Therefore, I did pretty much nothing but at the last second tried writing her a letter in Japanese which she said was really good, which I doubt.
Pretty much it's the same thing here. All of a sudden this cheesily touching cards come out (though I admit some were cute) and there all ads for all manner of household items that have the words 'Mother's Day' seemingly tacked on at the top.
Personally, later in the day my family and I visited some lady who owned a magnificent rose garden at the back of a shrine. I took some pictures just for the heck of it!