localised.cs

// picker

var picker = new Picker
            {
                HorizontalOptions = LayoutOptions.CenterAndExpand,
                WidthRequest = App.ScreenSize.Width * .8
            };
            picker.Items.Add(LangResources.LangEnglish);
            picker.Items.Add(LangResources.LangDanish);
            picker.Items.Add(LangResources.LangDutch);
            picker.Items.Add(LangResources.LangFrench);
            picker.Items.Add(LangResources.LangFrenchLU);
            picker.Items.Add(LangResources.LangGerman);
            picker.Items.Add(LangResources.LangItalian);
            picker.Items.Add(LangResources.LangNorwegian);
            picker.Items.Add(LangResources.LangPolish);
            picker.Items.Add(LangResources.LangRussian);
            picker.Items.Add(LangResources.LangSwedish);
            picker.SelectedIndex = 0;
            
            picker.SelectedIndexChanged += (object sender, System.EventArgs e) =>
            {
                selectedLang = picker.SelectedIndex;
                var cultureInfo = DependencyService.Get<ILocalize>();
                cultureInfo.CurrentUICulture = new CultureInfo("no");
                lblChooseLang.SetValue(Label.TextProperty, LangResources.Language);
            };
            
// ILocalize (android)

        public CultureInfo GetCurrentCultureInfo()
        {
            var androidLocale = Java.Util.Locale.Default;

            var netLanguage = androidLocale.ToString().Replace("_", "-");

            return new CultureInfo(netLanguage);
        }

        public void SetLocale()
        {
            var androidLocale = Java.Util.Locale.Default;
            var netLocale = androidLocale.ToString().Replace("_", "-"); 
            var ci = new CultureInfo(netLocale);

            Thread.CurrentThread.CurrentCulture = ci;
            Thread.CurrentThread.CurrentUICulture = ci;
        }

        public void SetLocale(string locale)
        {
            var netLocale = locale.Replace("_", "-"); 
            var ci = new CultureInfo(netLocale);

            Thread.CurrentThread.CurrentCulture = ci;
            Thread.CurrentThread.CurrentUICulture = ci;
        }

        public CultureInfo CurrentCulture
        {
            get
            {
                return Thread.CurrentThread.CurrentCulture;
            }
            set
            {
                Thread.CurrentThread.CurrentCulture = value;
            }
        }

        public CultureInfo CurrentUICulture
        {
            get
            {
                return Thread.CurrentThread.CurrentUICulture;
            }
            set
            {
                Thread.CurrentThread.CurrentUICulture = value;
            }
        }
        
  // ios
  
          public void SetLocale()
        {
            var iosLocaleAuto = NSLocale.AutoUpdatingCurrentLocale.LocaleIdentifier;
            var netLocale = iosLocaleAuto.Replace("_", "-");
            CultureInfo ci;
            try
            {
                ci = new CultureInfo(netLocale);
            }
            catch
            {
                ci = GetCurrentCultureInfo();
            }
            Thread.CurrentThread.CurrentCulture = ci;
            Thread.CurrentThread.CurrentUICulture = ci;
        }

        public void SetLocale(string locale)
        {
            var netLocale = locale.Replace("_", "-");
            CultureInfo ci;
            try
            {
                ci = new CultureInfo(netLocale);
            }
            catch
            {
                ci = GetCurrentCultureInfo();
            }
            Thread.CurrentThread.CurrentCulture = ci;
            Thread.CurrentThread.CurrentUICulture = ci;
        }

        public CultureInfo GetCurrentCultureInfo()
        {
            var netLanguage = "en";
            var prefLanguageOnly = "en";
            if (NSLocale.PreferredLanguages.Length > 0)
            {
                var pref = NSLocale.PreferredLanguages[0];

                prefLanguageOnly = pref.Substring(0, 2);
                switch (prefLanguageOnly)
                {
                    case "de":
                        pref = "de-CH";
                        break;
                    case "fr":
                        pref = pref == "fr" ? "fr-CH" : "fr-LU";
                        break;
                    case "it":
                        pref = "it-CH";
                        break;
                    case "nl":
                        pref = "nl-BE";
                        break;
                }

                netLanguage = pref.Replace("_", "-");
            }

            CultureInfo ci = null;
            try
            {
                ci = new CultureInfo(netLanguage);
            }
            catch
            {
                ci = new CultureInfo(prefLanguageOnly);
            }

            return ci;
        }

        public CultureInfo CurrentCulture
        {
            get
            {
                return Thread.CurrentThread.CurrentCulture;
            }
            set
            {
                Thread.CurrentThread.CurrentCulture = value;
            }
        }

        public CultureInfo CurrentUICulture
        {
            get
            {
                return Thread.CurrentThread.CurrentUICulture;
            }
            set
            {
                Thread.CurrentThread.CurrentUICulture = value;
            }
        }
        
  // myapp.cs (in the PCL)
  
  LangResources.Culture = DependencyService.Get<ILocalize>().GetCurrentCultureInfo();
  DependencyService.Get<ILocalize>().SetLocale();
            var currentLocale = DependencyService.Get<ILocalize>();
            currentLocale.CurrentUICulture = new CultureInfo("en");