Merge pull request #89 from smeinecke/fix/missing-i18n

Merging i18n fixes from @smeinecke. Thanks!

Notes for follow-up (will fix in v2.0.27):
- `toggleBtn.title = zhMode ? 'Switch to English' : '切换到中文'` introduces a hardcoded Chinese string that fails `node src/dashboard/check-i18n.js`. Will replace with `data-i18n-title` attribute pattern.
- The `error.${err.message}` lookup pattern is duplicated across 6 sites — will centralize into an `App.translateError(code, fallback)` helper next pass.
- Will also clean up the `action.revealKey` pre-existing miss while there.