Code review part I

CurrentWeather.vue

 <div class="row">
                {{ $t("WIND") }}:
                {{
                ** This ternary operator looks weird here, logic should be probably moved to function **
                  getWindDirection(weather.wind ? weather.wind.direction : 400)
                }}
                | {{ weather.wind ? weather.wind.speed : "n/a" }}m/s
              </div>

DailySummary.vue

** Would think about naming more appropiate than array. chartData?

get chartDataComputed() {
    let array = [];
    array.push(["Hour", "Temperature"]);
    array.push(
      ...(this.weather.forecast || []).map(f => {
        return [f.time, f.temp];
      })
    );
    return array;
  }

main.ts

import Vue from "vue";
import App from "./App.vue";
import router from "./router";
import VueI18n from "vue-i18n";
Vue.use(VueI18n);
import VueGoogleCharts from "vue-google-charts";

Vue.use(VueGoogleCharts);
import { languages } from "@/i18n";
import { defaultLocale } from "@/i18n";
const messages = Object.assign(languages);

Vue.config.productionTip = false;

var i18n = new VueI18n({
  locale: defaultLocale,
  fallbackLocale: "de",
  messages
});

new Vue({
  router,
  i18n,
  render: h => h(App)
}).$mount("#app");

** Good practice to import at the styles? **
import "fomantic-ui-less/semantic.less";
      

WeatherService.ts

export class SingleDayForecast {
  ** Why Date as string? You don't need any manipulations? **
  date?: string;
  averageWeather?: Weather;
  forecast?: Array<Weather>;
}
    
 const requestUrl =
    ** WHY NOT USE String interpolation?? **
    API_URL + "?id=" + cityId + "&units=metric" + "&APPID=" + API_KEY;