[new feature] add i18n support (#310)

* fix: Tabbar icon line-height

* [new feature] progress add showPivot prop

* [new feature] TabItem support vue-router

* [new feature] update document header style

* [Doc] add toast english ducoment

* [new feature] add i18n support

* feat: Extract demos from markdown

* feat: Base components demos

* [new feature] complete demo extract & translate

* [fix] text cases

* fix: add deepAssign test cases

* fix: changelog detail

* [new feature] AddressEdit support i18n

packages/locale/index.js

@@ -0,0 +1,45 @@
+import Vue from 'vue';
+import get from '../utils/get';
+import camelize from '../utils/camelize';
+import deepAssign from '../utils/deep-assign';
+import defaultMessages from './lang/zh-CN';
+
+// component mixin
+const i18n = {
+  computed: {
+    $t() {
+      const { name } = this.$options;
+      const prefix = name ? camelize(name) + '.' : '';
+      const messages = this.$vantMessages[this.$vantLang];
+
+      return (path, ...args) => {
+        const message = get(messages, prefix + path) || get(messages, path);
+        return typeof message === 'function' ? message.apply(null, args) : message;
+      };
+    }
+  }
+};
+
+const proto = Vue.prototype;
+const defaultLang = 'zh-CN';
+const locale = {
+  i18n,
+
+  init() {
+    Vue.util.defineReactive(proto, '$vantLang', defaultLang);
+    Vue.util.defineReactive(proto, '$vantMessages', { [defaultLang]: defaultMessages });
+  },
+
+  use(lang, messages) {
+    proto.$vantLang = lang;
+    this.add({ [lang]: messages });
+  },
+
+  add(messages = {}) {
+    deepAssign(proto.$vantMessages, messages);
+  }
+};
+
+locale.init();
+export default locale;
+export { i18n };