Replace i18n by a custom implementation (#638)

There are two problems with the current localization strategy:
- We download the translations on-demand, which means that it does a serial roundtrip for nothing.
- withTranslation helper actually renders the app 3 times on startup, instead of once (I haven't tried to debug it)

src/components/LanguageList.tsx

@@ -1,22 +1,20 @@
 import React from "react";
-import { useTranslation } from "react-i18next";
+import { t } from "../i18n";
 
 export function LanguageList<T>({
-  onClick,
+  onChange,
   languages,
   currentLanguage,
 }: {
   languages: { lng: string; label: string }[];
-  onClick: (value: string) => void;
+  onChange: (value: string) => void;
   currentLanguage: string;
 }) {
-  const { t } = useTranslation();
-
   return (
     <React.Fragment>
       <select
         className="language-select"
-        onChange={({ target }) => onClick(target.value)}
+        onChange={({ target }) => onChange(target.value)}
         value={currentLanguage}
         aria-label={t("buttons.selectLanguage")}
       >