feat(i18n): improve translations (#219)

Co-authored-by: 三咲智子 Kevin Deng <sxzz@sxzz.moe>
Co-authored-by: 沈青川 <46062972+ShenQingchuan@users.noreply.github.com>

components/user/UserSignInEntry.vue

@@ -1,10 +1,10 @@
 <template>
   <div p8 flex="~ col gap4">
     <div text-sm text-secondary>
-      Sign in to follow profiles or hashtags, favourite, share and reply to posts, or interact from your account on a different server.
+      {{ $t('nav_user.sign_in_desc') }}
     </div>
     <button class="btn-solid text-center" @click="openSigninDialog()">
-      Sign in
+      {{ $t('action.sign_in') }}
     </button>
   </div>
 </template>