I just see that the problem is also in the “next_post” and “prev_post” variable that are not taking account of the “hash-fr” or not but I don’t see where these variables are defined
{{!-- Links to Previous/Next posts --}}
<aside class="read-next outer">
<div class="inner">
<div class="read-next-feed">
{{#if primary_tag}}
{{#get "posts" filter="tags:{{primary_tag.slug}}+id:-{{id}}" limit="3" as |related_posts|}}
{{#if related_posts}}
<article class="read-next-card">
<header class="read-next-card-header">
{{#../primary_tag}}
<h3><span>{{#has tag="#fr"}}Plus dans{{else}}{{t "More in"}}{{/has}}</span> <a href="{{url}}">{{name}}</a></h3>
{{/../primary_tag}}
</header>
<div class="read-next-card-content">
<ul>
{{#foreach related_posts}}
<li>
<h4><a href="{{url}}">{{title}}</a></h4>
<div class="read-next-card-meta">
<p><time datetime="{{date format="YYYY-MM-DD"}}">{{date format="D MMM YYYY"}}</time> –
{{#has tag="#fr"}}{{reading_time minute="1 minute de lecture" minutes="% minutes de lecture"}}{{else}}{{reading_time minute=(t "1 min read") minutes=(t "% min read")}}{{/has}}</p>
</div>
</li>
{{/foreach}}
</ul>
</div>
<footer class="read-next-card-footer">
<a href="{{#../primary_tag}}{{url}}{{/../primary_tag}}">{{#has tag="#fr"}}{{plural meta.pagination.total empty="Aucun article" singular="1 article" plural="% articles"}}{{else}}{{plural meta.pagination.total empty=(t "No posts") singular=(t "1 post") plural=(t "% posts")}}{{/has}} →</a>
</footer>
</article>
{{/if}}
{{/get}}
{{/if}}
{{#has tag="#fr"}}
{{!-- If there's a next post, display it using the same markup included from - partials/post-card.hbs --}}
{{#get "posts" filter="tags:hash-fr+id:>{{id}}" limit="1" order="id asc"}}
{{#foreach posts}}
{{> "post-card-fr"}}
{{/foreach}}
{{/get}}
{{!-- If there's a previous post, display it using the same markup included from - partials/post-card.hbs --}}
{{#get "posts" filter="tags:hash-fr+id:<{{id}}" limit="1" order="id desc"}}
{{#foreach posts}}
{{> "post-card-fr"}}
{{/foreach}}
{{/get}}
{{else}}
{{!-- If there's a next post, display it using the same markup included from - partials/post-card.hbs --}}
{{#get "posts" filter="tags:hash-en+id:>{{id}}" limit="1" order="id asc"}}
{{#foreach posts}}
{{> "post-card"}}
{{/foreach}}
{{/get}}
{{!-- If there's a previous post, display it using the same markup included from - partials/post-card.hbs --}}
{{#get "posts" filter="tags:hash-en+id:<{{id}}" limit="1" order="id asc"}}
{{#foreach posts}}
{{> "post-card"}}
{{/foreach}}
{{/get}}
{{/has}}