Better late than never I guess, but you could try this:

public static string ResolveVortoValue(this string rawValue, CultureInfo currentCulture)
{
    VortoValue vortoValue;
    try
    {
        vortoValue = JsonConvert.DeserializeObject<VortoValue>(rawValue);
    }
    catch (Exception)
    {
        //wasn't valid json for VortoValue
        return rawValue;
    }            
    if (vortoValue == null) return rawValue;
    object resolvedValue;
    if (!vortoValue.Values.TryGetValue(currentCulture.Name, out resolvedValue)) return rawValue; //no value for currentCulture, also possible to check for other cultures if you want
    return resolvedValue.ToString();
}

EDIT: maybe I should've mentioned that I haven't tested this code, but it should get you going if it wouldn't work after copy-paste ;-)

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