If a character has a Japanese name, it's always used in place of the English name for the tag, regardless of which name is most familiar to the average user, right? Well why is this then not the case for Pokemon species, which are all technically character names? You can't say it's because those are the names we get first. If you want to say that people are just more familiar with the English Pokemon species names than Japanese, I'm willing to bet that the majority of Pokemon fans are more familiar with "Jessie" than "Musashi" but we still use the latter regardless. Yet at the same time we're left using blatantly English name tags like "Mr. Mime"?

Not complaining, I'm just wondering the reason for this strange inconsistency.

We get the vast majority of our tags from Danbooru and here is what Danbooru says:

As Jedi said, it's because of the sheer number of different pokemon. Also, a lot of the original Japanese pokemon names are already in use as general tags, since they're literally just English words. Here's a few examples:

Kakuna's Japanese name is the English word "Cocoon"
Beedrill's Japanese name is the English word "Spear"
Pidgeotto's Japanese name is the English word "Pigeon"
Sandshrew's Japanese name is the English word "Sand"
Clefable's Japanese name is the English word "Pixy"
Rapidash's Japanese name is the English word "Gallop"
Magnemite's Japanese name is the English word "Coil"
Doduo's Japanese name is the English word "Dodo"
Haunter's Japanese name is the English word "Ghost"
Krabby's Japanese name is the English word "Crab"
Chansey's Japanese name is the English word "Lucky"
Articuno's Japanese name is the English word "Freezer"
Zapdos's Japanese name is the English word "Thunder"
Moltres's Japanese name is the English word "Fire"

And that's just in the first 150. There are examples all down the list.

That’s a good point.
Almost all comments on this site are in English,
And most foreign comments are using the Latin alphabet, not the Japanese one.
Wouldn’t it be more user friendly if we used the English names?

We aren't going to use the English names for the human characters because we have a general policy of calling human characters by their original names in the series' original language. The actual Pokemon got an exception due to the sheer number of them to keep up with, but there's far fewer human characters with actual names.

Yeah my question was why the policy is that way.
It would me more user friendly if it wasn’t.

The most straightforward answer is because it's Danbooru's policy. Currently 70% of our content comes from Danbooru, tags and all.

We can't really use aliases for character names since they're irreversible, so if, say, the character's official English name changed (e.g. their last name gets revealed, their previous official name gets revealed to be a pseudonym, the official English publisher changed their mind on the spelling or something, etc) we'd be basically be stuck with whatever we used first. Keeping all character names (and copyright names - this same policy also applies to copyrights as well) changed to the English version is, to be blunt, impossible without aliases.

70% of our content comes in with original Japanese character and copyright names already tagged on them, so if we were to use the English names, there would immediately be a split, with two separate tags being used for the same thing, and the original Japanese name would have more than double the posts than the English name that's supposedly the correct tag.

If you want the policy changed here, you'll need to convince Danbooru first, since even if you got us to agree with you on that (which we don't), we couldn't change the policy until after they did.

Why are they irreversible?

Because the way our search index works. Reversing them isn't impossible, but it requires a rebuild of our search index, which would effectively take searching down for anywhere from a few hours to a couple days. Therefore, it would have to be something pretty major for us to go ahead and reverse an alias.