i18n\Formatter $numberFormatterSymbols

A list of name value pairs that are passed to the intl Numberformatter::setSymbol() method of all the number formatter objects created by createNumberFormatter(). This property takes only effect if the PHP intl extension is installed.

Please refer to the PHP manual for the possible options.

For example to choose a custom currency symbol, e.g. U+20BD instead of руб. for Russian Ruble:

[
    NumberFormatter::CURRENCY_SYMBOL => '₽',
]