while WarioWare Gold's dropped out of the 20 for all Japanese sales tracker, it's proven to have good legs and hasn't left the top 50 since launch. Unfortunately media create doesn't post numbers for games outside the top 20 so that leaves Dengeki Online, which has the game at
138k copies as of December 30.
For reference, here's how it compares to other 3DS games released in 2018:
Detective Pikachu: 94.203 (not counting sales of the 2016 "first chapter" release)
Persona Q2: 90,170
Etrian Odyssey Nexus: 89.764
Luigi's Mansion: 82,761
Captain Toad: 60.353
Mario & Luigi BIS remake: 10,839 (that's only one week of sale but that's still a really bad launch)
Sushi Striker: 2.652 (ouch!)
As you can see, it's not the only best selling new 3DS game for 2018 (though not the best-selling period, as both Mario Party Top 100 and Pokemon Ultra Sun/Moon sold more during the year), but the only one to break 100k at retail.
So yeah, while it's on track to be the lowest-selling game in the series after Game & Wario and the download-only games, it's a 3DS game released in mid-2018: context matters. Not a hit but not a flop, it should be profitable with its Japanese sales alone and its sales vis-a-vis other 2018 3DS games should show Nintendo the series still has life left in it despite the failure of Game & Wario and the nearly decade-long gap between games with "Made in Wario" in the title, and that a Switch entry could be succesful. The amount of promotion NCL has given to the game 4 months after the fact would also indicate to me they are satisfied with its performance.
If it helps contextualise its performance, the Mario & Luigi Superstar Saga remake sold a total of 71k despite coming out a year earlier in a completely dead week - and that was still enough to greenlit a sequel. So...