Localization for time?

Hi, i try to translate plugin to my language, but I find some words I can't change in lang files, and only way is edit code.
My language have many time forms, and i do solved it like that.

private static string FormatTime(TimeSpan time)
        {
            var values = new List<string>();

            if (time.Days != 0)
                if (time.Days == 1) values.Add($"{time.Days} dzień");
                else values.Add($"{time.Days} dni");

            if (time.Hours != 0)
                if (time.Hours == 1) values.Add($"{time.Hours} godzinę");
                else values.Add($"{time.Hours} godzin(y)");

            if (time.Minutes != 0)
                if (time.Minutes == 1) values.Add($"{time.Minutes} minutę");
                else values.Add($"{time.Minutes} minut(y)");

            if (time.Seconds != 0)
                if (time.Seconds == 1) values.Add($"{time.Seconds} sekundę");
                else values.Add($"{time.Seconds} sekund(y)");

            return values.ToSentence();
        }

Problem is with "values.ToSentence()". I try to find how to change last separator from "and" to "i", but is hard to find the solution in google. Can you help my? 'values.ToSentence(", ", " i ")' < I was trying this, but dosn't work.

.ToSentence() is provided by Oxide and I don't think it can be localized. Alternatively you can use 
return string.Join(", ", values.ToArray());​

 

which doesn't have the "and" at all.
Thanks for answer.