See forum #53259. We need to do something about this.
To fill in those unaware, the actual Pokemon creatures received are a rare exemption to the "use original names" policy beause the Japanese names (generally simple one-word names) are highly ambiguous and could conflict with a large number of other tags (especially artists). The English names are far less likely to be ambiguous given that a preponderance of names on Danbooru are Japanese(-ish).
This was all well and good for older Pokemon games that had English names established by the time we got around to setting a policy. But then newer games came out, and much fanart got posted before English names existed. So people used the Japanese names. The real killer here is that almost none of these names were qualified with _(pokemon) so now we have simple strings of Japanese syllables like giaru and shimama and mamepato (they'll be artists names some day, you just know it) to deal with.
Which unfortunately takes us back to the situation we wanted to avoid: a choice between 1) ambiguity concerns when aliasing to the English names for the sake of generally low-to-medium count creatures or 2) edits instead of aliases, leaving people stuck wondering which names to use and having to adjust as more English names trickle through.
Pokemon really, really need to be qualified, especially when we're using the Japanese names for new games. The extra typing is annoying but I can not see any way around this.
Updated by S1eth