fix(theme): add rel="alternate" and hreflang to links in language menu (#5108)

Author: tats-u

src/client/theme-default/components/VPMenuLink.vue

@@ -7,6 +7,7 @@ import VPLink from './VPLink.vue'
 
 const props = defineProps<{
   item: T
+  rel?: string
 }>()
 
 const { page } = useData()
@@ -33,7 +34,7 @@ defineOptions({ inheritAttrs: false })
       }"
       :href
       :target="item.target"
-      :rel="item.rel"
+      :rel="props.rel ?? item.rel"
       :no-icon="item.noIcon"
     >
       <span v-html="item.text"></span>

src/client/theme-default/components/VPNavBarExtra.vue

@@ -31,7 +31,13 @@ const hasExtraContent = computed(
       <p class="trans-title">{{ currentLang.label }}</p>
 
       <template v-for="locale in localeLinks" :key="locale.link">
-        <VPMenuLink :item="locale" :lang="locale.lang" :dir="locale.dir" />
+        <VPMenuLink
+          :item="locale"
+          :lang="locale.lang"
+          :hreflang="locale.lang"
+          rel="alternate"
+          :dir="locale.dir"
+        />
       </template>
     </div>
 

src/client/theme-default/components/VPNavBarTranslations.vue

@@ -19,7 +19,13 @@ const { localeLinks, currentLang } = useLangs({ correspondingLink: true })
       <p class="title">{{ currentLang.label }}</p>
 
       <template v-for="locale in localeLinks" :key="locale.link">
-        <VPMenuLink :item="locale" :lang="locale.lang" :dir="locale.dir" />
+        <VPMenuLink
+          :item="locale"
+          :lang="locale.lang"
+          :hreflang="locale.lang"
+          rel="alternate"
+          :dir="locale.dir"
+        />
       </template>
     </div>
   </VPFlyout>