Sets whether the translated text should lean towards formal or informal language.
This feature currently only works for target languages
DE (German),
FR (French),
IT (Italian),
ES (Spanish),
NL (Dutch),
PL (Polish),
PT-PT,
PT-BR (Portuguese)
and RU (Russian).
Setting this parameter with a target language that does not support formality will fail,
unless one of the prefer_... options are used.
Possible options are:
* default (default)
* more - for a more formal language
* less - for a more informal language
* prefer_more - for a more formal language if available, otherwise fallback to default formality
* prefer_less - for a more informal language if available, otherwise fallback to default formality