Validate a localised StringField and produce a localised error message.
validate : Form.Locale.Locale -> Form.Field.StringField -> Result Form.Validate.Types.StringFieldError Form.Field.StringField
Validator API for a StringField being valid.
errorToMessage : Form.Locale.Locale -> Form.Field.StringField -> Form.Validate.Types.StringFieldError -> String
Localised error message API for a StringField error.