Case-insensitive lang search for i8n, along with support for match just lang, without region, ie. 'en' == 'en-US'

src/i8n.ts

@@ -106,6 +106,13 @@ const translations: Record<LANG, Record<KEY, string>> = {
   },
 };
 
+const translationsLookup = Object.keys(translations).reduce((lookups, lang) => {
+  lookups.set(lang, translations[lang as LANG]);
+  lookups.set(lang.toLocaleLowerCase(), translations[lang as LANG]);
+  lookups.set(lang.toLocaleLowerCase().split("-")[0]!, translations[lang as LANG]);
+  return lookups;
+}, new Map<string, Record<KEY, string>>())
+
 export const randomLang = () => _.shuffle(["en-US", "nl-NL"])[0]!;
 
 export const asLANGs = (acceptLanguageHeader: string | undefined) =>
@@ -134,8 +141,8 @@ export const keys = (lang: LANG = "en-US") => Object.keys(translations[lang]);
 
 export default (serviceName: string): I8N =>
   (...langs: string[]): Lang => {
-    const langToUse =
-      langs.map((l) => translations[l as LANG]).find((it) => it) ||
+    const langToUse = 
+      langs.map((l) => translationsLookup.get(l as LANG)).find((it) => it) ||
       translations["en-US"];
     return (key: KEY) => {
       const value = langToUse[key]?.replace(

src/server.ts

@@ -87,7 +87,10 @@ function server(
   app.set("view engine", "eta");
   app.set("views", "./web/views");
 
-  const langFor = (req: Request) => i8n(...asLANGs(req.headers["accept-language"]))
+  const langFor = (req: Request) => {
+    logger.debug(`${req.path} (req[accept-language]=${req.headers["accept-language"]})`);
+    return i8n(...asLANGs(req.headers["accept-language"]));
+  }
 
   app.get("/", (req, res) => {
     const lang = langFor(req);

src/smapi.ts

@@ -536,9 +536,10 @@ function bindSmapiSoapServiceToExpress(
               .then(splitId(id))
               .then(({ musicLibrary, accessToken, type, typeId }) => {
                 const paging = { _index: index, _count: count };
-                const lang = i8n((headers["accept-language"] || "en-US") as LANG);
+                const acceptLanguage = headers["accept-language"];
+                const lang = i8n((acceptLanguage || "en-US") as LANG);
                 logger.debug(
-                  `Fetching metadata type=${type}, typeId=${typeId}, lang=${lang}`
+                  `Fetching metadata type=${type}, typeId=${typeId}, acceptLanguage=${acceptLanguage}`
                 );
 
                 const albums = (q: AlbumQuery): Promise<GetMetadataResponse> =>