add localisation support

currently only en_GB (TODO: dynamic language pack imports)

src/lib/lang.js

@@ -0,0 +1,60 @@
+import * as en_GB from '@cf/lang/en_GB.json';
+
+/**
+ * @param {string} lang IETH language tag (i.e. en_GB)
+ * @returns Map<string, string | string[]>
+ */
+export default function init(lang) {
+    let i18n = new Object();
+    let language;
+
+    // TODO: dynamic imports seem to fail here; it can't find the file.
+    // try {
+    //     language = import(`../lang/${lang}.json`);
+    // } catch (error) {
+    //     throw error;
+    // }
+
+    language = en_GB;
+
+    i18n.lang = language;
+    i18n.lang_code = lang;
+    i18n.string = function(/* @type string */ key) {
+        const tokens = key.split('.');
+        
+        let i = 0;
+        let token = tokens[i];
+        let res = this.lang;
+        while (true) {
+            res = res[token];
+            if (res === undefined) {
+                console.warn(`${key} not found for language ${this.lang_code}`);
+                return key;
+            }
+            if (typeof res === 'string' || res instanceof String)
+                return res;
+            i++;
+            token = tokens[i];
+        }
+    }
+    i18n.stringArray = function(/* @type string */ key) {
+        const tokens = key.split('.');
+        
+        let i = 0;
+        let token = tokens[i];
+        let res = this.lang;
+        while (true) {
+            res = res[token];
+            if (res === undefined) {
+                console.warn(`${key} not found for language ${this.lang_code}`);
+                return key;
+            }
+            if (Array.isArray(res))
+                return res;
+            i++;
+            token = tokens[i];
+        }
+    }
+
+    return i18n;
+}