I don't expect any article changes that state Kirby's gender being absolute as a result of my so-called evidence; I just thought maybe this would be an interesting topic to discuss. So as we know, Kirby's gender default to male in our language and various others which lack gender-neutral pronouns outside of "it." However, I'm not going to let that play much of a factor as to why I feel Kirby would be male. If anybody feels differently as to his gender, because you're allowed to think otherwise as that was the original intention, feel free to explain any points you may find valid.
So, here's why I choose to think Kirby is male outside of localization differences (I will still be using "he" as it's rather odd to call Kirby "it" for the entirety of the discussion). Kirby has some fairly masculine traits. While he may be pink, Miyamoto wanted him to be yellow, something that was less feminine. Kirby's pink, however, can also be associated with the phrase "tough guys wear pink." This was made still relevant in the Kirby Super Star Ultra commercial, ending on "He's the super tuff pink puff." Color aside, there have been some times we've seen a rather "buff" Kirby: the occasions in the anime, such as here, as well as even in Kirby and the Rainbow Curse where when having fun at the beach as seen here. You don't find girls with chests like that... at least, I don't think. Kirby is also greatly associated with vorarephilia, as he loves eating (not just food). This fetish seems to be more associated with guys than girls based on my knowledge.
Then there's sexuality. Initially, I'm going to assume Kirby is heterosexual. Kirby has been seen with some implied crushes, being ChuChu and Ribbon. His relationship with Elline is also strong, but whether or not there was some romance in that is less clear, to me at least, as I haven't played the game yet. Even his relationship with Tiff implies a bit: with Tuff, he's free-roam and having fun, like driving go-karts, getting chocolate bars, or causing havoc to make predictions come true. With Tiff, he can be a bit more mature, and she's the only one of all characters to be able to summon the warp star; however the differences in behaviors may just be a result of the respective character's personality, with Tiff being generally more mature, with Tuff being noticeably less so.
Another issue is helpers. They're all confirmed to be male from what I know, or at least none are female. Meta Knight, Dedede, and Waddle Dee are also confirmed male. Despite this, they go on with mouth-to-mouth. While this may just be similar to CPR, the manga makes it a gag clearly referencing kissing; kissing is also referenced in Kirby Fighters Deluxe, as sharing food makes the word "smooch" appear. However, Meta Knight, as well as Dedede and Waddle Dee, also can do this to each other, despite all of the above having confirmed genders. However, while this may imply bisexuality/pansexuality to some, I think I'm just going to dismiss it as Nintendo logic (I'm not that kind of Game Theorist anyway); although I'm still unsure about the whole "smooch" bit.
Due to the relations with ChuChu, or more importantly Ribbon, Kirby is likely not homosexual, as he probably wouldn't be blushing and falling down stairs if he was kissed from the opposite gender. Kirby could still be bisexual/pansexual though, because, let's face it, Japan is weird. Aside from gender differences with Spinni, there's also Birdo. If you don't know the story, Birdo, in its first appearance, was a guy, and a transgender. Birdo wanted to be a girl. This was almost certainly awkward to discover at the time; this was even mentioned in its Melee trophy. However, as far as I'm concerned, Birdo is presumably female now in certain localizations and the transgender thing was dropped... that or Birdo's wish came true, aside from not being "Birdetta."
Kirby could also simply not have a gender, like earthworms (just not Jim). Kirby may have some sexual preferences, but maybe not an actual gender. He shows no sexual parts and has been assumed by some to reproduce through mitosis; however, not having any apparent "parts" doesn't necessarily mean anything. Donkey Kong and Diddy Kong go around practically nude, but you don't see anything there. We really don't know what the heck Kirby is outside of an extraterrestrial, which is why we still choose to speculate.