rails: Couldn't find template for digesting: Error when calling a dynamically named partial

I am having an issues when trying to cache dynamically named partials which include static content

In site.html.erb I call:

<% cache("#{@site.name}_#{locale}", :expires_in => 2.hour) do %>
    <%= render partial: "my_#{@site_name}_#{locale}" %>
<% end %>

Error

Couldn't find template for digesting: pages/my_#{@site_name}_#{locale}
Cache digest for app/views/pages/site.html.erb: 493b4a427278b191dc524264e105ea52

The partial is located in the same directory as site.html.erb and is e.g. named as follows: pages/_my_nice_page_en.html.erb or pages/_my_nice_page_de.html.erb

It looks like if rails looks at the wrong place for partials and or does not evaluate the dynamic string assignment and thus can’t assign a digest to a missing partial and thus cannot cache the partials.