WARNING: Invalid Babel locale: 'zh-tw'. [i18n.babel]

[rffontenelle]

The warning message is shown 5 times for each languages with code containing country part. This can be found in meta page. This currently applies to pt-br, zh-cn, zh-tw and hi-in.

It also applies to gr locale, but it is because it should be el as per python/docsbuild-scripts#248 (comment).