hepburn.csv

hepburn.js

const wanakana = require('wanakana');
const fs = require('fs');
const toId = require('../../Pokemon-Showdown/sim/dex-data').Tools.getId;

const contents = fs.readFileSync('hepburn.csv', 'utf8');
const lines = contents.split('\n');

let i = 0;

const aliases = {};
for (let line of lines) {
  i++;
  if (i === 1) continue; // header
  const fields = line.split(',');
  const romajiID = toId(wanakana.toRomaji(fields[2]));
  const english = fields[1];

  aliases[romajiID] = english;
}

for (let romajiID in aliases) {
  let english = aliases[romajiID];
  if (romajiID !== toId(english)) {
    console.log(`\t"${romajiID}": "${english}",`);
  }
}

Toukyou: Long vowels may be written to replicate the hiragana spelling: long o is usually ou, long e usually ei, the others are doubled.

I see the problem:

long o is usually ou, long e usually ei, the others are doubled.

"Usually" is not "always". In katakana, i.e. in Pokémon names, "ō" and "ē" are usually written "oo" and "ee".

But this is also not a 100% thing. For instance, Ho-oh is hōō, but this is "houou", not "hoooo".

You have to go directly from katakana to romaji, you can't go from Modified Hepburn to Wapuro Hepburn directly because Modified Hepburn loses information.