Make mentions-timeline use i18n.

src/components/mentions/mentions.vue

 <template>
-  <Timeline :title="'Mentions'" v-bind:timeline="timeline" v-bind:timeline-name="'mentions'"/>
+  <Timeline :title="$t('nav.mentions')" v-bind:timeline="timeline" v-bind:timeline-name="'mentions'"/>
 </template>
 
 <script src="./mentions.js"></script>