extract messages with --flatten causes issues when there are multiple plural rules using hash placeholder

[aquark]

extract messages with --flatten causes issues when there are multiple plural rules using hash placeholder

[longlho]

@formatjs/cli throws an error when --flatten is used with multiple plural or select. Since you're using it programmatically maybe you wanna set throws: true as well?
This is something we don't plan to support in the near future since multiple plurals are not supported by most TMSes. In your example, smartling purposefully also does not support multi-plurals: https://help.smartling.com/hc/en-us/articles/360008030994-ICU-MessageFormat
Multiple plurals yield a LOT of resulting strings since it basically has to explode all the combos of plural forms, take ru for example:
1 plural = 4 different sentences
2 plurals = 16 (4^2) different sentences
3 plurals = 64 different sentences

I'd suggest you rewrite your message.