Defining custom localization without momentJS

[HellFriend0]

Hello, I got a question on which I didn't find an answer so far.

I am working on a project and using vis-timeline. I used localization via momentJS but for better optimalization I tried something like this:

visTimeline.moment.defineLocale("sk", {
            months: "Január_Február_Marec_Apríl_Máj_Jún_Júl_August_September_Október_November_December".split("_"),
            monthsShort: "Jan_Feb_Mar_Apr_Máj_Jún_Júl_Aug_Sep_Okt_Nov_Dec".split("_"),
            weekdays: "Nedeľa_Pondelok_Utorok_Streda_Štvrtok_Piatok_Sobota".split("_"),
            weekdaysShort: "Ned_Pon_Uto_Str_Štr_Pia_Sob".split("_"),
            weekdaysMin: "Ne_Po_Ut_St_Št_Pi_So".split("_")
});

var options = {
            locale: "sk",
            ...
};

Translation work but I got warning
WARNING: options.locales['sk'] not found. See https://visjs.github.io/vis-timeline/docs/timeline/#Localization

Is there any way how to get rid of this warning ?