Unable to trigger render when switching between multiple objects containing content in different languages - vue.js

Question

I read Reactivity in Depth but can't solve the issue.
I'm creating a small single page app that contains images and text.
When the user clicks a button I want the language to change.
Currently I am storing the content in two files that export an object.
export default {
projects: [
{
title: 'Project Title',
year: 2016,
...
},
]
}
and importing that
import contentEn from './assets/content.en.js'
import contentDe from './assets/content.de.js'
new Vue({
el: '#app',
components: { App },
data: {
mainContent: {
content: contentEn
}
},
methods: {
switchToGerman(){
this.mainContent.content = contentDe
}
},
template: '<App :mainData="mainContent"/>',
})
When I assign another object to mainContent.content the rendering is not triggered.
I understand that adding and deleting properties from object don't lead to change detection but I switch out a whole object. I tried assigning it with this.$set with no success.
I also tried this and googled a lot but can't get it work.
Or is my approach just wrong?
Thank you for helping,
best,
ccarstens
EDIT:
See below the code for the App component and the ProjectElement
// App.vue
<template>
<div id="app">
<button #click="switchGerman">Deutsch</button>
<ProjectElement v-for="(project, key) in fullData.content.projects" :key="key" :content="project"/>
</div>
</template>
<script>
import ProjectElement from './components/ProjectElement'
export default {
name: 'App',
props: [
'mainData'
],
data () {
return{
fullData: {}
}
},
methods: {
switchGerman(){
this.$root.switchToGerman()
}
},
created(){
this.fullData = this.$props.mainData
},
watch: {
mainData: {
handler: function(newData){
this.fullData = newData
},
deep: true
}
},
components: {
ProjectElement,
}
}
</script>
And the ProjectElement
//ProjectElement.vue
<template>
<article :class="classObject" v-observe-visibility="{
callback: visibilityChanged,
throttle,
intersection: {
threshold
}
}">
<header v-html="description"></header>
<div class="content">
<carousel :per-page="1" :pagination-enabled="false">
<slide v-for="(slide, index) in projectContent.media" :key="index">
<VisualElement :content="slide" ></VisualElement>
</slide>
</carousel>
</div>
</article>
</template>
<script>
import {Carousel, Slide} from 'vue-carousel'
import VisualElement from './VisualElement'
export default {
name: "ProjectElement",
components: {
Carousel,
Slide,
VisualElement
},
props: [
'content'
],
data () {
return {
projectContent: {},
isVisible: false,
throttle: 300,
threshold: 0.8
}
},
created(){
this.projectContent = this.content
},
methods: {
visibilityChanged(isVisible){
this.isVisible = isVisible
}
},
computed: {
description(){
return `
<p>${ this.projectContent.title } - ${this.projectContent.year}</p>
<p>${ this.projectContent.description }</p>
`
},
classObject(){
return {
visible: this.isVisible,
'project-element': true
}
}
}
}
</script>

Answer 1

Did you try doing deep copy:
switchToGerman () {
const copyContent = JSON.parse(JSON.stringify(this.mainContent))
copyContent.content = contentDe
this.mainContent = copyContent
}

Answer 2

I found the solution (thank you #EricGuan for pointing out that the mistake must lay somewhere else)
As you can see in the original post I created a watcher for the mainData property and expected that this would trigger the re render.
What was missing is, that I didn't watch the content property on the ProjectElement component, thus not triggering a re render there.
I added this to ProjectElement.vue and now it works like a charm:
watch: {
content(newContent){
this.projectContent = newContent
}
},
Thank you everybody for helping me! <3