How to use a custom format for chart series values

You can use a custom format pattern to apply to this series value, similar to the  ICU pattern set. Use something like #,### to get 1,234 as output, or $# to add dollar sign before digits. Pay attention that if you use % percentage format then your values will be multiplied by 100.

Is it possible to show dots instead of comma (Ex.: 14.500,00)?

The charts use ICU patterns. And, it is not possible to reverse the decimal and thousand separators, unfortunately. Here's what it says, "Illegal patterns, such as "#.#.#" or "#.###,###", will cause DecimalFormat to set a failing UErrorCode.". Source: http://icu-project.org/apiref/icu4c/classicu_1_1DecimalFormat.html.